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VESUVIUS 
Eruption of April, 1906. Emission of gas, ashes, and sand as seen from the Observatory. 



MAURY-SIMONDS PHYSICAL GEOGRAPHY 



PHYSICAL GEOGRAPHY 



BY 
M. F. MAURY, LL.D, 

LATE OF THE NAVAL OBSERVATORY, WASHINGTON, D.C. 

REVISED AND LARGELY REWRITTEN 
BY 

FREDERIC WILLIAM SIMONDS, Ph.D. 

PROFESSOR OF GEOLOGY IN THE UNIVERSITY OF TEXAS 



oJOic 



NEW YORK •:■ CINCINNATI •:• CHICAGO 

AMERICAN BOOK COMPANY 



^^' 



[library orcONQRE^ 
Two Copies Receivea ' 
jAN 14 1908 
Copyri«ni tmrj» 

5LASSA XXC. No. 

Copy's. 



Copyright, 1908, by 
FREDERIC WILLIAM SIMONDS. 

Entered at Stationers' Hall, London. 



MAURY-SIMONDS PHYS. GEOG. 



PREFACE 

The advance of geographic sciende has been so great during 
the last decade that a thorough- revision of the older text-books 
has become imperative. To the end that Maury's Physical 
Geography may maintain its position, it has been the writer's 
privilege not only to revise, but largely to rewrite that well- 
known book. In so doing an attempt has been made to pre- 
serve as far as possible the plan of the older work — a plan 
that has met the approval of a generation of teachers — and, 
at the same time, to modernize the text thoroughly. 

In the matter of illustrations, the present volume will be 
found exceedingly attractive and the adoption of a smaller page 
will add much to the reader's comfort. 

In the preparation of this edition, acknowledgments are 
due to many persons, especially to Dr. William J. Battle and 
Dr. WiUiam T. Mather of the University of Texas — the 
former, for the use of some of his excellent photographs of 
Egyptian scenery ; the latter, for timely suggestions which 
have added materially to the accuracy of the text. Acknowl- 
edgments are also made to Mr. Sterling R. Fulmore for Ha- 
waiian, Australian, and New Zealand views ; to Professor A. J. 
Henry, of Washington, D.C., for cloud views ; to Mr. W. E. 
Seright, of Stafford, Kansas, for the unique photograph of a 
tornado ; to President D. S. Jordan, of Leland Stanford Junior 
University, for CaHfornia earthquake views ; and to Professor 

5 



6 • PREFACE 

H. L. Fairchild, of the University of Rochester, for photo- 
graphs of drumlins, kames, and eskers. The diagrams and 
most of the maps have been drawn by the writer or, under 
his direction, by Mr. N. P. Pope. 

FREDERIC W. SIMONDS. 
The University of Texas, Austin. 



CONTENTS 



PAGE 

Introductory 9 



PART L — THE EARTH 

CHAPTER 

I. The Earth and the Solar System ii 

II. The Shape, Size, and Density of the Earth . . i8 

III. The Motions of the Earth 23 

IV. Terrestrial Magnetism 32 

V. Internal Heat of the Earth 40 

VI. Volcanoes 46 

VII. Earthquakes 60 

PART IL— THE LAND 

VIII. The Land Masses . .70 

IX. Relief of the Land 75 

X. Relief Forms of North and South America . . 95 

XI. Relief Forms of Europe, Asia, Africa, and Australia 114 

XII. Islands 128 

PART III. — THE WATER 

XIII. Properties of Water 136 

XIV. Waters of the Land 140 

XV. Drainage .......... 165 

XVI. The Sea and the Oceans 171 

XVII. Waves, Tides, and Currents 179 

7 



CONTENTS 



PART IV. — THE ATMOSPHERE 

CHAPTER 

XVIII. Physical Properties of the Atmosphere 



PAGE 
200 



XIX. Climate 

XX. Atmospheric Circulation 

XXI. Storms 

XXII. Moisture of the Air 

XXIII. Rain 249 

XXIV. Hail, Snow, and Glaciers ...... 258 

XXV. Electrical and Optical Phenomena .... 275 



210 
218 
229 
239 



PART v. — LIFE 

XXVI. Animals and Plants 

XXVII. The Distribution of Useful Plants 

XXVIII. The Distribution of Animals 

XXIX. Man 

XXX. Geographical Distribution of Labor 



280 
288 
292 

311 

322 



APPENDIX 
XXXI. Physical Geography as a Science 



328 



INTRODUCTORY 

Physical Geography deals with the world in the present stage 
of its existence. It considers the machinery which makes day 
and night, seedtime and harvest ; which lifts the vapor from 
the sea, forms clouds, and waters the earth ; which clothes the 
land with verdure and cheers it with warmth, or covers it with 
snow and ice. Physical Geography, moreover, treats of the 
agents that cause the wonderful circulation of waters in the 
sea ; that diversify the continents with mountains, hills, plains, 
and valleys, and embelUsh the landscape with rivers and lakes. 
It views the earth — its surface, its waters, and its enveloping 
atmosphere — as the scene of operation of great physical forces, 
which by their united action render possible the life of plants 
and animals ; and studies the life of the globe, both terrestrial 
and aquatic, noting particularly the circumstances which are 
favorable or adverse to its development. 

It has been found convenient to present the topics treated in 
the following order : — 

I. The Earth. 

II. The Land. 

III. The Water. 

IV. The Atmosphere. 
V. Life. 





JUPITtR^^02BlT0£j>^ ^> 



of neptune _ 
The Solar System 



PART I. — THE EARTH 



I. THE EARTH AND THE SOLAR SYSTEM 

The Solar System. — By the ancients the earth was regarded 
as the center of the universe. Men saw the sun in the same 
part of the heavens morning after morning, and when his light 
faded at night they saw the stars in nearly the same positions 
as on the preceding night. Hence they concluded that the 
sun and stars all move around the earth once in 24 hours. 
Careful observation seemed to confirm this idea. Astronomers 
watched the heavens ; they mapped the stars ; they recorded, 
from night to night, the places of the brightest among them. 
As a result, they found that the position of some remains 
unchanged with reference to that of their companions, while 
the position of others varies perceptibly. 

The former were called Jixed stars; the latter received the 
name planets, from a Greek word meaning wanderers. For 
several centuries, however, astronomers have known that the 
ancient idea was a mistake. The sun, not the earth, is the 
center around which the planets revolve, and the earth itself 
is a planet. The planets are not self-luminous, but shine by 
reflected sunlight. Their paths of motion, or orbits, are nearly 
circular, and they all journey around the sun in nearly the same 
plane. In their regular order, beginning with that nearest to 
the sun, the planets are Mercury, Venus, Earth, Mars, Jupiter, 
Saturn, Uranus, and Neptune. 

With the exception of Mercury and Venus, they are attended 
by one or more moons, or satellites. The sun, planets, and 
satellites, together with a number of small planetary bodies 



12 THE EARTH AND THE SOLAR SYSTEM 

called asteroids, or pla^ietoids, which revolve in paths between 
Mars and Jupiter, constitute the Solar System, so named from 
the Latin sol, the sun. 

Within the limits of the Solar System there are also comets and meteoric 
swarms. The former are celestial bodies usually consisting of a head, with a 
very bright spot which gradually shades into a less luminous portion, or coma, 
and a tail, or streamer. 




GiACOBiNi's Comet, December 29, 1905 

From photograph by Professor E. E. Barnard, Yerkes Observatory. 

Owing to the movement of the camera, which was kept focused on the comet during the 
exposure, the stars appear as hues instead of points. 

Comets seem to be composed of matter in a highly rarefied state, for even 
small stars are visible through them. Some, from their movements around 
the sun, must be considered members of the Solar System ; others appear as 
casual visitors, passing never to return. 




The Henderson, North Carolina, Meteorite 

Two views. From proceedings of the U. S. Nat. Mus., Vol. 32. 

13 



14 



THE EARTH AND THE SOLAR SYSTEM 



The meteoric swarms seem, in some instancies, to follow the orbits of cer- 
tain comets ; in others, the number of meteors is so great as apparently to fill 
the entire circuit of their own orbits. In either case, when they encounter 
the atmosphere of the earth, there is a brilliant display of shooting stars, the 
so-called meteoric showers. 

The Sun. — The sun is also a star. From it the planets derive 

both heat and light. This vast ball, or sphere, is more than a 

million times as large as the earth. Were the earth placed 

at the sun's center, 

Q\SV^ ' 

the latter body would 

reach so far into space 
as to extend nearly 
200,000 miles beyond 
the orbit of the moon, 
or almost 440,000 
miles beyond the 
earth's surface. 

The sun is in an 
intensely heated con- 
dition, and clouds of 
incandescent gases 
project outward from 
its surface for thou- 
sands of miles into 

Diagram showing the Comparative Sizes of space. From examina- 
THE Earth, the Orbit of the Moon, and ,- 1 ..1 ,, 

THE SUN'S DISK tions made with the 

spectroscope it is 
known to contain many substances entering into the composition 
of the earth. 

Origin of the Solar System. — The sun and the planets are 
composed of the same kinds of matter and have similar forms 
and motions. Many astronomers and philosophers have tried 
to combine these facts and others into an explanation of the 
origin of the Solar System. Such explanations are termed 
hypotheses. Of these hypotheses at least two merit attention ; 
namely, the nebular and the planetesimal. 




THE NEBULAR HYPOTHESIS 



15 




Diagrammatic Illustration of the Nebular Hypothesis 

Showing the abandoned rings in various stages. 5 is the central sun ; a, b, c, successive 
rings; d, e,f,g, denser portions of certain rings which, in the process of planet forma- 
tion, are drawing the less dense portions within themselves. 

The Nebular Hypothesis. — This hypothesis, which apparently 
fails to meet some of the necessary physical tests, assumes a vast 
glowing cloud, or nebula, of gaseous matter extending beyond 




Saturn and his Rings 



the orbit of the farthest planet and endowed with a slow rotary 
motion. As this nebula cooled and contracted, its rotation 



i6 



THE EARTH AND THE SOLAR SYSTE.M 



became more rapid and it became disklike in form. As the 
contraction continued, partial or complete rings similar to the 
rings of Saturn were separated from the outer edge. These, 
contracting toward their densest parts, became planets, revolv- 
ing around the central nucleus, which we call the sun. 

The Planetesimal Hypothesis. — This hypothesis assumes the 
sun as the origin of the planets. Attracted by an approaching 
star, a sun wave of gaseous matter flew off forming, with the 




Relative Sizes of the Sun and Planets 

The names of the planets are indicated by their initial letters except Mercury and Mars 

which are indicated by My and Ms respectively. 



central nucleus, a spiral nebula. This cooled and condensed into 
small separate particles (planetesimals) like the meteoric dust 
that sometimes falls upon the earth. Some of these particles, 



THE EARTH AND THE UNIVERSE 1 7 

colliding and uniting, formed small bodies, which were enlarged 
by continual showers of planetesimals and thus became planets. 

The Relative Sizes of the Sun and Planets. — The relative 
sizes of the sun and planets are shown in the cut on page i6, in 
which the diameter of the sun has been reduced to 3^ inches. 
It has been calculated that the sun contains 600 times the 
united volumes of all the bodies revolving about it. Even the 
larger planets are greatly inferior to it in size, while the smaller 
planets are comparatively insignificant. 

If the earth be represented by a globe one foot in diameter, 
the sun must be represented by a sphere 35 yards in diameter, 
placed 2 1 miles from the globe, in order to show in proper pro- 
portion the size of the two bodies and the distance between 
them. In a similar manner Jupiter, the largest planet, would 
be represented by a globe 3| yards in diameter at the distance 
of 1 1 miles from the sun. 

The Earth and the Universe. — From the astronomer we learn 
that most of the fixed stars are possibly the suns of other systems 
resembling our own, but in many cases vastly larger. From 
him we also learn that the heavens are filled with unknown 
numbers of such systems. Hence follows the conclusion not 
only that the earth is one of the smaller members of the solar 
system but that the solar system is itself one of the numerous 
systems that fill the immensity of space. With this in mind it 
is possible to realize that tJie earth is an exceedingly small part 
of the created universe. 

The subordinate position of the Solar System is strongly suggested by the 
face that, under the influence of the other suns of the universe, it appears to 
be moving through space in the direction of the constellation Hercules. 



M.-S. PHYS. GEOG. — 2 



II. THE SHAPE, SIZE, AND DENSITY OF THE 

EARTH 



Shape of the Earth. — As inhabitants of the earth we are 
greatly impressed with its surface irregularities. What a con- 
trast betv/een lofty summits of the Andes or Himalaya mountains 




Diagram illustrating the Curvature of the Earth 

and the depths of the ocean basins ! Can a body exhibiting 
so many and so great inequalities fall within the boundary 




Diagram illustrating the Curvature of the Earth by the increased range 
of vision in ascending a height. 

of a regular geometric form ? We are merely suffering from 
the nearness of the view. Could we station ourselves on the 



SHAPE OF THE EARTH 



19 



moon, then as we beheld the earth, its surface irregularities 
would no longer confuse us. In comparison with the whole 
they would sink into insignificance, and the earth would appear 
as a great rounded globe or sphere not varying in its general 
shape from the other planets. 

There is ample proof that the surface of the earth is curved. 

I. Watch ships as they sail seaward. Do they not pass over a curved 
surface as their hulls, then their sails, and lastly their topmasts, disappear from 
view ? 




An Eclipse of the Moon 

From photograph by G W. Ritchey, Yerkes Observatory. 

Partial phase of the total eclipse of October 16, 1902, 10 : 33 P.M. The margin of 
the earth's shadow is curved. 



2. Stand at the foot of a hill overlooking a plain and note the boundary 
line or limit of vision. Now climb to the summit and note the increased 
range of vision. Were the earth flat, this would not occur. 

3. Observe the curved margin of tlie earth's shadow during an eclipse of 
the rrioon. 

The sun, earth, and moon being now in the same straight line, the shadow 
of the earth extends in the form of an elongated cone far beyond the orbit of 
the moon. That body, in the course of its movement, cuts this shadow which 



20 



THE SHAPE, SIZE, AND DENSITY OF THE EARTH 



obscures its face. While the margin of the shadow is ill defined, it is, never- 
theless, sufficient to show the general curvature of the surface. 
That the earth is of a spherical shape is also shown — 

1. By voyages and journeys "■ round the world." 

2. By the measurement of arcs of great circles. 

3. By the fact that the horizon when viewed from a high point rising above 
a level plain, as from a tower or the summit of a hill, is always circular, a 
property belonging only to spherical bodies. 

The Earth an Oblate Spheroid. — The particles of a rotating 
body tend to fly off in straight lines. This tendency is called 

centrifugal force. 
Gravitation tends to 
make a mass spher- 
ical. These two 
forces combined 
have caused the 
earth, v^^hich is some- 
what plastic and 
elastic, to assume a 
slightly flattened 
spherical form called 
an oblate spheroid. 
Its longest diameter 
is nearly 7927 miles 
and its shortest di- 
ameter nearly 7900 
miles. Its greatest 
circumference is 
about 24,900 miles, 
its smallest circum- 
ference about 24,860 
miles, and the area of 
its surface 197 mil- 
lions of square miles. 




Diagram for demonstrating the Spheroidal 
Form of the Earth 

The horizon when viewed from a high point, A, B, or C, 
is a circle 



The oblateness of the earth is shown by the fact that although the weight 
of a body on its- surface is nearly constant, it is slightly greater in high 
latitudes. 



DENSITY OF THE EARTH 



21 



Density of the 
Earth. — The exterior 
is the only part of the 
earth concerning 
which we have definite 
knowledge. Here we 
encounter matter in 
its three forms : the 
gaseous, represented 
by the atmosphere ; 
the liquid, represented 
by the hydrosphere, 
or water areas ; and 
the solid, represented 
by the lithosphere, 
or " crust." These 
spheres are arranged 
in the order of their 
densities, and although 
the air and water are 
often spoken of as the 
earth's coverings, they 
are as much of the 
planet as the litho- 
sphere. 

On account of pres- 
sure each of these 
spheres should become 
denser in the direction 
toward the center of 
the earth. The bot- 
tom of the atmosphere, 
especially that part 
resting on the sea, is 
densest, as it is com- 
pressed by the weight 




JUPITER 



SATURN 



NEPTUNE 



URANUS 



(^ EARTH 
(^ VENUS 
The Planets arranged according to Size 



© MARS 
Q MERCURY 



22 



THE SHAPE, SIZE, AND DENSITY OF THE EARTH 



of the air above it. Similarly, the water in the deepest parts 
of the sea should be densest, but water is practically a non- 
compressible medium. It does not seem unreasonable that the 
materials constituting the lithosphere should increase in density 




Section of the Earth , 
A, atmosphere; B, hydrosphere ; C, Hthosphere ; N, nucleus. 

toward the earth's nucleus or centrosphere, which must be the 
densest part of all. That such is the fact appears to be proved 
by numerous experiments which go to show that while the 
density of the outer portion of the lithosphere is about 2.5, 
that of the lithosphere and nucleus together is not far from 5.5. 



III. THE MOTIONS OF THE EARTH 

Effects of the Earth's Motions. — The earth has two motions 
which greatly influence all things living upon it, whether animals 
or plants. The first is a daily motion, or rotation on its axis, 
by which there is produced an alternation of light and darkness 
called day and night. The second is a yearly motion, or revolu- 
tion about the sun, by which seasonal changes are produced and 
the many consequences flowing from them. 

Meridians. — When the sun reaches its highest point for the 
day, the shadow cast by a plumb line extends north and south. 
Hence north-and-south lines are called mcridia7is, or midday 
lines. All meridians when produced meet at the ends of the 
earth's axis, called the poles. The meridian of any place can 
be determined roughly by means of a vertical rod on a level 
table. Beginning about half an hour before midday, mark 
at intervals of two minutes the end of the shadow cast by the 
rod till the shadow lengthens. The line from the end of the 
shortest shadow to the base of the rod points north and south 
and lies in the meridian of the; place. 

Parallels. — Lines at right angles to any meridian extend 
east and west. Since they are parallel circles around the earth, 
they are called parallels. The parallel midway between the 
poles is called the equator, since it divides the earth into two 
equal parts, or hemispheres. 

Position. — The position of a place is determined when we 
know its distance north or south of the equator and its distance 
east or west of a standard meridian. 

Latitude and Longitude. — The distance north or south from 
the equator, measured in degrees along a meridian, is called 
latitude. The latitude of the equator is o°, and of the poles 

23 



24 



THE MOTIONS OF THE EARTH 



NORTH 
STAR * 









90°, the highest latitude. Distance east or west from a stand- 
ard meridian measured in degrees along a parallel is called 
longitude. The meridian of Greenwich, near London, is com- 
monly taken as the standard. The longitude of the Greenwich 
meridian is 0°, and the longitude of the most distant meridian is 
180°. The sun crosses all meridians, that is, 360° of longitude, 
every 24 hours, at the rate of 1 5° an hour. Hence the difference 

in longitude between two places is 
equal to 15° multiplied by the dif- 
ference in time in hours. The differ- 
ence in time can be determined by 
means of accurate timekeepers com- 
monly called chronometers, and by 
telegraph. The length of a degree 
of longitude is about 68.7 miles at 
the equator and decreases gradually 
to o at the poles. 

Measuring Latitude. — The line of 
the earth's axis passes close to a star 
in the northern heavens called the 
North Star or the polestar. To an 
observer at the equator, the polestar 
seems to be at the horizon. As he 
travels northward it seems to rise in 
DIAGRAM SHOWING THE Posi- ^hc heavcus a degree for every 
TioN OF THE NORTH STAR dcgree of latitude till at the pole, 
IN THE HEAVENS 90° N., It is iu tho zeiiith, or 90° above 

the horizon. In other words, the latitude of a place north of 
the equator may be found by measuring the altitude of the 
polestar. 

At the equinoxes (see p. 26) the sun is directly over the 
equator, and on these dates the latitude of a place is equal 
to the angular distance from the zenith to the midday sun. 

The Problem of Eratosthenes. — In 240 b.c. Eratosthenes, a 
famous Greek astronomer, measured an arc of a meridian by 
means of the noon shadow. He found that the angular differ- 




REVOLUTION 2$ 

ence between the sun's altitude at Syene, in Egypt, and its 
altitude at Alexandria, 5000 stadia north of Syene, was 7° 12'. 
On this basis he computed the earth's circumference to be 
250,000 stadia, or about 24,000 miles. 

Rotation. — The sun always illumines the half of the earth 
turned toward it, leaving the other half in darkness. Owing, 
however, to the rotation of the earth once in 24 hours, all 
points upon its surface, with the exception of limited areas 
near the poles, are during that period brought alternately into 
sunlight (day) and immersed in darkness (night). 

The earth rotates from west to east. In consequence of this a jooint on its 
surface, as New York, crosses the boundary between the darkened and lighted 
hemispheres, or the great circle of illumination, and the sun is seen to rise in 
the east. An hour later the same phenomenon is observed by the people of 
Saint Louis, and two hours later by the people of Denver. In each of these 
places the sun appears to rise higher and higher in the heavens until the 
meridian or midday point has been reached, and then it begins to recede 
toward the western horizon, and finally disappears or sets. As the sun rises 
in New York an hour before its appearance in Saint Louis it likewise sets in 
New York an hour earlier, and for a similar reason it sets in New York two 
hours earlier than in Denver. 

An interesting evidence of the earth's rotation is that suggested by Newton. 
It is easy to see that a body at the top of a tower will, if the earth really ro- 
tates, move with greater velocity than will the base of the tower. Let a ball 
be dropped from the top of such a tower, and, if not deflected by the air, it 
will strike a point on the ground some distance from the foundation. The 
experiment is of little practical value, for it is difficult to calculate the deflec- 
tion caused by the air. 

Revolution. — The passage of the earth around the sun, or its 
revolution, requires 365^^ days. This constitutes the time inter- 
val known as a year. The path of the earth around the sun is 
not a perfect circle, but an ellipse having the sun in one of its 
foci. While the axis of the earth constantly points in the same 
direction whatever may be its position in its orbit, it is inclined 
to the plane of that orbit 66^°, or 23^° from the perpendicular. 
To this is due the varying lengths of day and night and the 
changes of the seasons. 



26 



THE MOTIONS OF THE EARTH 



The nearer a planet is to the sun, the more rapidly it revolves, and the 
shorter is its year. The year of Mercury, the nearest planet, is only 88 days 
long; Jupiter's year consists of about 12 of ours; Neptune's of more than 
160. 

Variations in the Lengths of Day and Night. — Let 5 represent 
the sun (see diagram) and the arrows the direction of the earth's 
motion in its orbit. When the earth is at A it will be seen that 

















Diagram showing the Position of the Earth at Four Points in its Orbit 
A, the vernal equinox ; B, the summer solstice ; C, the autumnal equinox ; D, the 

winter solstice. 



the direct rays of the sun fall upon the equator and that the great 
circle of illumination passes exactly through the poles. Day 
and night in all parts of the world are therefore equal. This 
occurs on March 21, which is called the vernal eqinnox. The 
earth, continuing its passage around the .sun, reaches the position 



VARIATIONS IN THE LENGTHS OF DAY AND NIGHT 27 

B in its orbit. The direction and inclination of its axis remain- 
ing the same, it will be seen that the direct rays of the sun have 
apparently moved north and that they now fall upon the Tropic 
of Cancer. Moreover, as the sun always illumines one half of 
the earth, the entire region within the arctic circle is in daylight, 
while the corresponding region within the antarctic circle is in 
darkness ; that is, during the passage of the earth from A to B 
the great circle of illumination has changed its position so that 
instead of passing through the poles it now passes through two 
alternate points 23-^-° from the poles. 

As the great circle of illumination passes beyond the north 
pole, the days in the northern hemisphere constantly increase in 
length, until at B, the summer solstice, or June 22, there is ex- 
perienced the longest day and the shortest night of the year. 
On the other hand, in the southern hemisphere the opposite 
conditions prevail. During the passage of the earth from A to 
B the days grow constantly shorter, and the nights longer ; thus 
in the two hemispheres there is an alternation in the lengths of 
the periods of light and darkness. 

At C the sun's rays fall again directly upon the equator, the 
great circle of illumination passes through the poles, and the 
days and nights are equal. This is the autiiDinal equinox, or 
September 22. 

At D the direct sun rays fall upon the Tropic of Capricorn, 
and the great circle of illumination reaches only the arctic circle, 
but in the southern hemisphere sunlight extends beyond the 
pole to the antarctic circle. It will be seen that the conditions 
which prevailed when the earth was at B are completely re- 
versed. Then the northern hemisphere experienced its longest 
day and its shortest night, now the southern hemisphere has 
its longest period of light and its shortest period of darkness. 
This is the winter solstice, or December 21. 

The length of days and nights varies with the latitude. At the equator, or 
0°, they are always equal; that is, twelve hours long. At latitude 30.8° the 
longest day is 14 hours ; at latitude 58.5°, 18 hours ; at latitude 63.4°, 20 hours ; 
at latitude 66.5°, 24 hours. Within the arctic or antarctic circles the longest 



28 THE MOTIONS OF THE EARTH 

day or greatest period of sunlight exceeds 24 hours, being in latitude 67.4°, i 
month ; in latitude 73.7°, 3 months ; in latitude 90°, 6 months. 

The arctic day and the arctic night have been thus described by an eye- 
witness : — 

" The sun moves quickly in these latitudes from the first day he peers over 
the horizon in the south until he circles round the heavens all day and all 
night ; but still quicker do his movements seem when he is on the downward 
path in autumn. Before you know where you are he has disappeared and the 
crushing darkness of the arctic night surrounds you once more. 

''On September 12 we should have seen the midnight sun for the last time 
if it had been clear and no later than October 8 we caught the last glimpse 
of the sun's rim at midday. Then we plunged into thg longest Arctic night 
any human beings have ever lived through in about 85 north latitude. Hence- 
forth there was nothing that could be called daylight, and by October 26 
there was scarcely any perceptible difference between day and night." — Report 
of Captain Otto Sverdrup, Appendix to Nanseii's Farthest North. 

Sidereal and Solar Days. — It is the rotation of the earth on 
its axis that gives rise to the time divisions in common use. 
The time of a rotation of the earth can be measured accurately 
by means of the stars, and is called a sidereal day, from the Latin 
sidus, 2L star. It is the time unit used by astronomers. The 
time between two successive noons is called an apparent solar 
day. As the earth rotates it moves onward in its path around 
the sun, faster as it approaches the sun, and slower as it recedes. 
Hence apparent solar days are somewhat longer than sidereal 
days, and vary slightly in length. The average length of ap- 
parent solar days is called a mean solar day and is the common 
unit of time. It is divided into two series of 12 hours each, one 
beginning at midnight and the other at noon. 

Standard Time. — Before the advent of railroads and the 
telegraph each community used the mean solar time of its own 
meridian. As communication between distant points became 
frequent and rapid, it became necessary to have a simpler time 
system. Hence, in 1883, the railroads agreed to use a system 
of standard time. By this plan the United States is divided 
into four time sections, each of which uses the mean solar time 
of its standard meridian. These meridians are 15° apart and 
their times are an hour apart. 



CHANGE OF SEASONS 29 

The Julian and the Gregorian Calendars. — The earth revolves 
around the sun in about 11 minutes less than 365 1 days. 
Hence a calendar year of 365 days is shorter than the solar 
year. In order to make the calendar year more accurate, Julius 
Caesar in 46 B.C. decreed that each fourth year (leap year) 
should contain 366 days. This coiTection was too great, and in 
1582 the error amounted to nearly half a month. In that year 
Pope Gregory XIII partially corrected the error by suppressing 
10 days in the calendar. He also made a rule which keeps 
the calendar practically correct. By this rule every year of 
which the number is divisible by 4 without a remainder is a 
leap year excepting years divisible by 100, which are leap years 
only when divisible by 400. Thus 1600 was a leap year; 1700, 
1800, and 1900 were common years ; 2000 will be a leap year ; 
and so on. The Gregorian calendar, or New Style, was not 
adopted in England till 1752, when Parliament enacted that the 
day following September 2 of that year should be called Sep- 
tember 14. 

Change of Seasons. — As already shown (page 26), when the 
earth is at A sunshine extends from pole to pole, and day and 
night are of equal length everywhere in the world. As the 
direct rays of the sun at this time fall upon the equator, the heat 
there is of the greatest intensity, decreasing polewards in the two 
hemispheres as the inclination at which they strike the surface 
increases. This is illustrated on page 30. Let A, B, and C 
represent three sunbeams or rays striking the earth in three 
different places. On account of the remoteness of the sun they 
are practically parallel, but owing to the curvature of the earth 
they are cut by its surface at different angles. The beam A 
falling upon the equator warms an area equal to its cross section ; 
the beam B falling in a latitude north of the equator warms an 
area of greater size than its cross section, hence a diminished 
temperature ; the beam C striking the earth at a higher latitude 
warms a still greater area, but with a further diminution of tem- 
perature. There is, moreover, a loss in the heating power of 
the sun's rays occasioned by their passage through the atmos- 



30 



THE MOTIONS OF THE EARTH 



phere — the more inclined the rays, the greater becomes the 
atmospheric distance to be traversed and the greater the loss 

of heat. (Compare 
the atmospheric dis- 
tances traversed by 
the beams A and B.) 
The warming of 
the earth when in the 
position A (page 26) 
produces the condi- 
tions known as spring 
in the northern hemi- 
sphere and autumn 
in the southern. As 
the earth advances in 
its orbit toward B, 
on account of the in- 
clination of its axis 
•toward the sun, the 
direct rays or beams 
steadily move toward 
the north until at B 
they fall 23.^° north 
of the equator. The 

Ti^optc of Ccinccv is 
Diagram illustrating the Manner in which the ^ -^ 

Sun's Rays penetrate the Atmosphere and tncrcfure the nortlieni 
strike upon the Earth's Surface in Differ- //;;^// ^y ^/^^ direct sun 
ENT Latitudes 

j^ajfs. 

With the increased length of day in the northern hemisphere, 
which has already been explained, comes an increase of heat 
and those conditions known as summer, while, on the other 
hand, the diminution of heat effects, due to the presence of the 
direct sun rays north of the equator and the shortening of the day, 
produce in the southern hemisphere the cold or winter season. 

As the earth moves toward the position C in its orbit, the 
direct rays of the sun recede from the Tropic of Cancer, the 




CHANGE OF SEASONS 3 1 

northern hemisphere gradually cools until the conditions at A 
are repeated ; that is, day and night are of equal length, the 
direct rays fall upon the equator, and neither hemisphere is 
favored at the expense of the other. Thus in the northern 
hemisphere the summer season passes into autumn, while in the 
southern the wintry days have given way to those of spring. 

When the earth has reached the point D in its orbit, the pole 
is inclined away from the sun, and the direct beams having 
moved south of the equator now fall 23^° south of that great 
circle. The Tropic of Capricorn is therefore the southern limit 
of the direct sim rays. The summer of the southern hemi- 
sphere has arrived and the northern hemisphere has entered 
upon the winter season. 



IV. TERRESTRIAL MAGNETISM 

Magnetism of the Earth. — To the earth as a whole belong 
certain properties of a magneto-electric character, not yet fully- 
understood, which are the source of much scientific interest 
as well as of great practical value. The importance of the 
discovery of magnetism and the invention of the compass can 
scarcely be estimated. Without that instrument navigation 
would be practically impossible and the determination of direc- 
tion over wide areas of the earth's surface futile. While mag- 
netism falls more properly within the domain of physics, the 
fact that the earth acts as a weak magnet suffices also to bring 
that subject within the scope of physical geography. 

Magnetism. — Among the ores of iron there is a variety of 
the mineral magnetite known as lodestone, which possesses the 
power of attracting to itself filings or other small pieces of iron. 
Such a body is called a magnet, and the influence that it exerts 
over other bodies is called magnetism. If a needle or a bar of 
steel be rubbed with lodestone, this property of the natm-al magnet 
will be imparted to it, and the needle or bar of steel becomes an 
artificial magnet. The property of magnetism also appears in 
a bar of soft iron or steel forming the core of an insulated coil 
of copper wire through which an electric current is passed, but 
with the cessation of the current the magnetic property disap- 
pears. Such a temporary magnet is termed an electro-magnet. 

Polarity. — If a bar magnet or a horseshoe magnet be placed 
beneath a sheet of paper upon which iron filings have been 
sprinkled and the paper gently tapped, the iron particles will 
arrange themselves about the extremities of the magnet in the 
greatest abundance, leaving the shape of the magnet well out- 
lined upon the paper. The extremities of the magnet, where 

32 



THE EARTH AS A MAGNET 33 

the attraction is greatest, are termed the poles, and the area 
through which the magnetic influence is felt, the magnetic field. 
A comparison of the effects of each pole upon the fiHngs would 
apparently lead to the conclusion that the two poles are identi- 
cal, but a simple experiment will serve to show that they are 
different. 

Let two common needles be magnetized and each suspended 
by a thread attached to its middle point by a bit of wax. 
These needles will tend to arrange themselves in a north-and- 
south direction. If their north ends or poles be marked and 
made to approach each other, it will be found that between 
them there is exerted a repellent force ; likewise, that between 
the south ends of the needles there is also repulsion. On the 
other hand, it may be readily shown that between the north 
pole of one needle and the south pole of the other there exists 
an attractive force. The general law governing this phenom- 
enon is as follows : Like poles repel, unlike poles attract. 

About halfway between the north and south poles, along a 
line crossing the magnet, the opposite magnetic forces are neu- 
tralized. This is known as the neutral line. 

If a piece of iron, or a magnetic needle, be suspended exactly 
over this line, it will not be attracted at all. On either side of 
it, however, a suspended needle is drawn toward one or other 
of the poles. The exact position of the neutral line depends on 
the relative strength of the poles. As these are seldom if ever 
of equal strength, the neutral line will rarely or never be equi- 
distant from both. 

The Earth a Magnet. — In some very important respects the 
earth behaves like a magnet. 

In the first place it displays attractive poiver precisely similar 
to that of the magnet. It is terrestrial magnetism which causes 
magnets to point northward when suspended. 

Secondly, like the magnet, the earth has magnetic poles. ' These 
are not exactly at the north and south geographical poles, but at 
some distance from them. They are the points at which the 
needle stands vertical. The north magnetic pole is in North 

M.-S, PHYS, GEOG. — 3 



34 



TERRESTRIAL MAGNETISM 



America. It is situated in Boothia, latitude 70° 5' north, longi- 
tude 96° 45' west. The discovery of this pole was made by Sir 
James Ross in 1831. 

The position of the 
south magnetic pole has 
not been so accurately 
determined. Sir James 
Ross reached a point in 
the Antarctic Ocean where 
the inclination was 88"^ 35', 
from which its situation 
has been computed. It is 
not, however, diametrically 
opposite the north mag- 
netic pole, but far to one 
side. It lies in the vicinity 
of lat. 75° S., long. 138'' E. 
The positions of these 
poles are constantly chang- 



Thirdly, the earth, 
like a magnet, has a 
neutral line. This 
line encircles the 
globe about midway 
between the north and 
south'magnetic poles. 
Along it the opposite 
polar forces counter- 
act each other. It is 
called the niasrnetic 




The Earth as a Magnet 
The vertical arrow at the left of the north geographic pole 
points to the north magnetic pole. The vertical arrow 
at the right of the south geographic pole points to the 
south magnetic pole (which is in the hemisphere turned 
from the reader and therefore not directly opposite eOltCltOV. ItS GOUrSC is 
the north magnetic pole). , j a-t, u 4- 

"^ ^ ' traced upon the chart. 

Inclination or Dip of the Needle. — In passing northward from 
the magnetic equator the north end of the needle is drawn 
downward more and more from a horizontal position until the 
north magnetic pole is reached, where, as already stated, it 
points vertically. In like manner, in going southward from 




35 



36 TERRESTRIAL MAGNETISM 

the magnetic equator, the needle is drawn downward until 
at the south magnetic pole it should again point vertically, 
although reversed in position. (On page 3.4 the needle is repre- 
sented in the form of an arrow. At the north magnetic pole 
the head of the arrow is directed downward ; at the south mag- 
netic pole, the shaft.) 

Inclination, or dip, may be represented on a chart by drawing 
lines in the northern and southern hemispheres connecting all 
points in which the ajigle of dip is of the same value. 

Such lines are usually termed isoclinic lines, but by some 
authors they have been called magnetic parallels. The line 
connecting points having no dip is, of course, the magnetic 
equator. In the eastern hemisphere it lies to the north of the 
geographic equator, but in the western, for the most part, to 
the south. 

Declination of the Needle. — While magnets free to move as- 
sume a north-and-south direction, they do not point exactly to 
the true geographical north, but a little to the west or the east 
of it. The deviation from the true northerly position is called 
the declination of the needle. 

The direction in some places is east, in others west. It will be seen from 
the map that over about one half of the globe it is easterly, over the other 
half westerly. 

The amount of declination varies in different localities, being 
much greater in some than in others. This may be presented 
to the eye in two ways : First, by drawing on the same chart 
both the true and the magnetic meridians. The latter have 
been defined as " the lines along which one would travel were 
he to set out at any place on the earth and always follow the 
compass needle." As the magnetic poles, through which the 
magnetic meridians pass, do not coincide with the geographic 
poles of the earth, a greater or less variation in the two sets of 
meridians is inevitable. 

Second, by drawing lines on a chart passing through those 
places having the same declination. Such lines, called isogenic 




37 



38 TERRESTRIAL MAGNETISM 

lines, must not be confused with the magnetic meridians. Just 
as there is a magnetic equator along which there is no dip or 
horizontal deviation, so there are lines, known as agonic lines, 
along which there is no decHnation. On the accompanying 
chart (page 37) both the isogonic and the agonic lines are 
shown. In the western hemisphere the agonic line, passing 
from the north magnetic pole southeastward through Hudson 
Bay and Canada, enters the United States near the eastern 
end of Lake Superior, and, after traversing the intervening 
states in a general southeast direction, leaves the country not 
far below the city of Charleston in South Carolina. Eastward 
of this line the declination is to the west ; westward of this line 
the declination is to the east. This is indicated on the chart by 
the use of broken and unbroken lines. 

Variations in Declination. — The intensity and position of the 
forces which cause the needle to deviate from the true north- 
and-south direction are constantly changing. Hence arise what 
are known as variations in declination. 

Secular variations extend over long periods. The declination at London 
was east in 1580, and amounted to 11° 15'; in 1657 it was zero; in 1818 it 
attained its maximum, 24° 38' 25", and was west. In 1877 it had decreased 
to 19° 22' 22" west. It is therefore decreasing at the rate of about 5' an- 
nually ; so that in about 200 years it should be east again. 

Diurnal variations also occur. They are eastward and westward oscillations 
of the needle, caused every day by the sun. The extreme eastward deflection 
is reached at about 8 a.m., the westward at about 2 p.m. The movements 
observed at the same hour in the northern and southern hemispheres are 
opposite in direction. 

Diurnal variation is almost zero at the equator. In the northern hemi- 
sphere it is greatest at the time of the summer solstice, least at the winter 
solstice. 

Magnetic Storms. — To certain " spasmodic variations " in the 
earth's magnetism, which are plainly indicated by the behavior 
of the needle, the term magnetic storms has been applied. 
Their duration may vary from a moment to several days. 
Often they are attended by electrical display such as auroras. 
While their coming seems to be somewhat irregular, a relation 



GENERAL CONCLUSIONS 39 

has been noticed between these disturbances and solar activity 
— that for those years in which the sun spots are most numerous 
magnetic storms are most frequent and of greatest violence. 
The " spot period " of the sun is a little over eleven years, from 
minimum to maximum, say five years ; from maximum to mini- 
mum, six years. 

"In November, 1882, near the period of maximum sun spots, a magnetic 
storm occurred which caused the magnetic needle at Los Angeles, Gal., to 
move over i^° out of its normal position. There was at the time a brilliant 
auroral display. The storm occurred over the entire earth, at Los Angeles, 
Toronto, London, St. Petersburg, Bombay, Hongkong and Melbourne, and 
began practically at the same instant of absolute time.''' — L. A. Bauer. 

General Conclusion. — The phenomena above described show 
conclusively that the earth is a great though rather feeble mag- 
net. But whether its magnetism results from magnetic bodies 
located within its mass (permanent magnetism), or, as some 
have thought, from the generation of electric currents, due to 
its unequal heating during rotation (electro-magnetism), is not 
yet fully determined. 

" All modern investigations would seem to lead to the conclusion that there 
exists both a very deep-seated magnetic field and one confined to a compara- 
tively thin layer, and that the earth's total magnetism results from systems 
of electric currents as well as from permanent and induced magnetizations." 

— L. A. Bauer. 



V. INTERNAL HEAT OF THE EARTH 

Evidences of Internal Heat. — While the surface temperature 
of the earth's crust ranges from about 80° Fahrenheit at the 
equator to possibly 0° F. at the poles, there are good reasons for 
believing that the earth's interior is intensely hot. As bearing 
upon this subject the evidence furnished by deep mines, hot 
springs, geysers and artesian wells, and volcanoes will be con- 
sidered. 

Mines. — In his search for mineral wealth man has penetrated 
far into the earth's crust. In many parts of the world his 
operations have been carried on by means of deep shafts, and 
in no instance has he failed to note an increase of temperature 
for an increase of depth below the surface. A comparison of 
observations made in widely separated localities shows that the 
rate of increase is not altogether uniform, but varies with the con- 
ductivity, or power to transmit heat, of the rocks encountered, 
and is, moreover, modified by local conditions, as proximity to a 
volcano or a mass of igneous rock not yet thoroughly cooled. 

Omitting exceptional cases, the average rate of increase, for 
depth below the line unaffected by surface heat or cold (line of 
no variation), seems to be 1° F. for about 65 feet. ' 

In boring the Saint Gotthard tunnel, between Italy and Switzerland, the 
temperature increased at the rate of 1° F. for 82 feet, and in boring the Mont 
Cenis tunnel, between Italy and France, at the rate of 1° F. for 79 feet. 

As illustrating the extremes of variability two unusual cases may be cited. 
As the result of careful observation at the celebrated Calumet-Hecla copper" 
mine on the south shore of Lake Superior it has been found that for the depth 
of 4939 feet the average increase of temperature is 1° F. for 103 feet. 

On the other hand, unusually high temperatures have been experienced 
at the Comstock lode, Virginia City, Nev., as, for example, 130'' F. at the 
depth of 2000 feet or an increase of 1° F. for 15.4 feet of descent, and at the 
Gold Hill mines on the same lode waters entered the 3000-foot level at a 

40 



HOT SPRINGS 41 

temperature of 170° F., which would give an average of 1° F. for 28 feet. 
These high temperatures may be due to the decomposition of rocks contain- 
ing feldspar. 

Artesian Wells bear testimony to the same rapid increase of 
heat. These have been sunk in various parts of Europe and 
America to a depth -varying from 1000 to 4000 feet. 

The rate of increase in the temperature varies in different 
places. The average is 1° F. for 50 to 70 feet. The temperature 
of the well at Crenelle, near Paris, is 81.7° F. Its depth is 1798 
feet. That at Budapest is 3160 feet deep. Its temperature 
is 178° F. It supplies a part of the city with warm water. 
An artesian well at Marlin, Tex., 3330 feet in depth, has a 
temperature of 147° F. 

Experience shows that by boring artesian wells, warm water 
may be obtained in almost every region of the earth. 

Hot Springs. — Hot or //^^/7^rt/ springs occur in all parts of the 
world. While more abundant in volcanic regions, they are by 
no means confined to the vicinity of volcanoes. The thermal 
springs of Bath, England, having a mean temperature of 120°, 
are 900 miles from the Icelandic volcanoes, over 1000 miles 
from Vesuvius and Etna, and fully 400 miles from the extinct 
volcanic region of France. 

As to the source of the heat manifested by hot springs there 
is reason to believe in many instances that it is local, as in the 
case of springs occurring in regions of active and extinct vol- 
canoes. There are, however, thermal springs, breaking out 
along the line of deep fissures, in which the source must be 
regarded as "deep-seated," and there are still other cases in 
which chemical action may be urged as the source of heat. 
Hot springs, it seems, afford evidence of the existence of sub- 
terranean heat, but they furnish meager data for establishing 
its rate of increase for depths below the surface. 

On the Island of Saint Michael, one of the Azores, there are some remarkable 
hot springs. Here the waters rising through volcanic rocks become charged 
with silica (the substance of quartz), which, upon reaching the surface, on ac- 
count of cooling, they precipitate, or deposit, in the form of sinter. As these 



42 



INTERNAL HEAT OF THE EARTH 



waters act as a petrifying medium, grasses, ferns, and other forms of vegetation 
are seen about the basins in various stages of mineralization. 

An excellent example of the deposit of carbonate of lime is afforded by the 
terraces of Mammoth Hot Springs, Yellowstone National Park. It is thought 
that the precipitation here may in part be due to the action of algae (low 
forms of plant life), to which also may be attributed the brilliant colorings, 
scarlet, blue, green, noticed upon freshly forming surfaces. 

Geysers. — The term geysers or gtisJiers is applied to certain 
periodically eruptive hot springs occurring in limited areas in 




Ml.\Lk\A iLKUACL, A Hoi Sl'RING DETOSI F, VELLOWSTUNE NATIONAL PaKK 

The substance of this beautiful terrace is travertine or carbonate of lime. By its deposi- 
tion from hot waters numerous basins have been built up which now contain pools of 
various temperatures. From photograph by Haynes. 

regions of active or dying volcanic energy. The most noted 
are those of the Yellowstone National Park in northwestern 
Wyoming, Iceland, and New Zealand. 

The distinguishing characteristic of a geyser is an eruption 
during which hot water and steam are ejected with more or less 
violence from a craterlike opening or basin which is connected 
below with a pipe or conduit leading downward into the earth. 
The water is heated to a high temperature ; that of the Great 
Geyser in Iceland is 212° F. at the surface, but in the lower 



VOLCANOES 43 

portion of the tube the thermometer indicates 266°. By the 
relief of pressure, due to the overflow of the basin, the super- 
heated waters rising toward the surface suddenly flash into 
steam, thus producing an explosion or eruption by which a 
column of water and steam is projected far above the vent. 

Like ordinary hot springs, geysers afford evidence of the 
existence of heat below the earth's surface, but the source of 
the heat is evidently volcanic. 

About the mouths of geysers there are often found highly ornamental incrusta- 
tions, consisting of silica and other minerals which are soluble in the geyser 
water while it is hot, but are deposited as it cools. The basins or craters vary 
in size from a few inches to many feet in diameter and height. That of the 
Great Geyser in Iceland is four feet in depth and 72 feet in diameter. In the 
center of this basin is a pipe or funnel eight feet wide. Out of this funnel 
water nearly boiling constantly issues. Eruptive discharges also occur. Of 
these there are certain premonitions. Underground rumblings are heard, 
the water in the basin boils furiously, and a domelike mass of hot water with 
clouds of steam is thrown 40 or 50 feet high. 

One or more of these minor discharges occur, and then succeeds a grand 
eruption. With a rumbling that shakes the ground, another column of 
boiling water 90 to 100 feet high is forced into the air with loud explosions 
and amid clouds of steam. Then out through the top of this column smaller 
jets are driven to marvelous heights above it. The pipe is thus emptied of 
water. But at once it begins to fill up, only to be emptied again by another 
grand explosion. 

Of the Yellowstone geysers an observer says : — 

"Of all the geysers whose eruptions v/e witnessed, the Grand was, I think, 
the most interesting. It played each evening at a regular hour. Suddenly 
it shot a vast stream of water over 200 feet into the air. This was maintained 
for a few minutes ; then it ceased, and the waters shrank back into the cav- 
ernous hollow below. Meanwhile subterranean thunder shook the ground, 
and after a minute's cessation another eruption occurred," 

Volcanoes are the most striking of all manifestations of the 
earth's internal heat. They are so important that they will 
be considered in detail in a subsequent lesson. Here, however, 
it is proper to observe what strong confirmation they afford to 
the theory of subterranean heat. Streams of lava, white-hot, 
like molten iron; issue through their craters from the interior of 



44 



INTERNAL HEAT OF THE EARTH 









A Geyser in Eruption 

" Old Faithful," Yellowstone National Park. This celebrated geyser received its name 
from the regularity of its eruptions, which occur at intervals averaging 65 minutes. 
The discharge lasts five or six minutes, the column of steam and water reaching the 
height of 90 to 100 feet. From photograph by Haynes. 



CONDITION OF THE INTERIOR OF THE EARTH 45 

the earth, together with steam and other heated vapors, hot 
ashes, and stones. 

Condition of the Interior of the Earth. — The phenomena 
above considered have suggested the conclusion that the inte- 
rior of the earth is in a fluid state and that only to the depth of 
from 30 to 40 miles is the crust of the earth soUd. 

It is argued that if the heat increase for depths below the 
surface at the rate noted in mines and deep borings, then at 
a comparatively shallow depth even the most refractory sub- 
stances must necessarily be in a state of fusion. This view, it 
will be observed, is in accord with the nebular hypothesis. 

Most scientific men, however, doubt the fluidity of the central 
mass, and admit the existence only of local reservoirs of molten 
rock. They contend that, instead of being fluid, the interior of 
the earth, though intensely hot, is pasty, or even solid. In 
support of this they argue that the enormous pressure exerted 
upon the interior of the earth would nullify the effect of its 
internal heat; for if a substance be subjected to pressure, it can- 
not melt so readily as under ordinary conditions. A body, 
therefore, may remain solid at a very high temperature, if under 
pressure.* In consequence of this the state of the successive 
layers constituting the earth is such that while they are sub- 
jected to a heat which increases enormously as the center is 
approached, they are at the same time subjected to a pressiwe 
which also increases enormously as the center is approached. 

Whether, however, we adopt the view that the central mass 
is fluid or solid, it does not affect the conclusion that it is in an 
intensely heated condition. 

* This is applicable to substances which contract when they solidify ; ice and a 
few other substances, which expand upon solidification, have their melting points 
lowered by pressure. 



VI. VOLCANOES 

What is a Volcano ? — To this question there are two answers : 
The first is that of the geographer; the second, that of the 
geologist. 

(i) The term volcano is usually applied to a mound, hill, or 
mountain composed of rocky materials ("lava," "cinders," 
"ashes," etc.) ejected from the earth's interior through a tube 
or opening in the crust. The upper end of this conduit is in 
a bowl-shaped depression, called a crater, which may be on the 
summit or slope of the ejected mass. As typical volcanoes are 
ordinarily more or less conical, it is customary to speak of vol- 
canic cones. 

(2) But as defined by Professor Judd, volcanoes are not neces- 
sarily "mountains" at all. "Essentially they are just the re- 
verse — namely, holes in the earth's crust, or outer portion, by 
means of which communication is kept up between the surface 
and the interior of our globe." 

Kilauea, on an island of the Hawaiian group in the North Pacific Ocean, on 
account of the gi^eat size of its crater, is one of the most remarkable volcanoes 
of the world. Its external opening, on the flanks of Mauna Loa, is in the 
form of a basin nearly 1000 feet deep. This great crater has a width of two 
miles, a length of three miles, and a circumference of eight miles. 

Formation of Volcanic Cones. — If at its beginning a volcano is 
simply a hole in the earth's crust, the form assumed by the 
cone will depend very much upon the character of the material 
ejected. Should it be in a very liquid state, like melted glass 
or iron, then the cone will rise at a low angle from a spreading 
base as seen in the Hawaiian volcanoes. Should, however, the 
material be viscous, like pitch, the cone will rise at a steeper 
angle and will assume somewhat of a dome shape. Again, 

46 



HEIGHT OF VOLCANIC CONES 4/ 

should the material ejected be fragmental, as ashes and cin- 
ders, the cone will rise at a rather high angle and take on 
the form seen in Cotopaxi and Chimborazo. The inclination 
or slope of a mixed cone, that consisting of both molten and 
fragmental materials ejected from the same vent, will, in large 
degree, depend upon the kind of material predominating, being 
steeper for the fragmental and less steep for the molten. 

Submarine Volcanoes. — The formation of a volcano may begin 
at considerable depths below the level of the sea. In proof of 
this it may be said that vast numbers of oceanic islands owe 
their existence to volcanic action, and deep-sea soundings show 
that many of the deepest parts of the ocean are covered with 
volcanic debris. 

In 1 83 1 a mass of matter accompanied by a discharge of steam rose from 
the sea near the coast of Sicily, and attained in a few weeks the height of 200 
feet above the water. It had a circumference of about three miles and was named 
Graham Island. In a few months, however, it disappeared, as the materials 
composing it, being loosely held together, were unable to withstand the 
action of the waves. 

Height of Volcanic Cones. — Volcanic cones vary much in 
height. Some are but slightly elevated, less than 500 feet ; 



i~ 




^^^^i^^^^^-r:— S^ 


■^ 



Small Cone near Outer Rim of Mauna Loa 

others tower skyward many thousand feet. The latter do not 
attain this great height through the accumulation of ejected 
matter alone, but are usually situated in highly elevated plateau 
or mountainous regions, as is conspicuously shown in the case 



48 



VOLCANOES 



of the higher volcanoes of the Andes. Here are cones Hke 
Aconcagua, in Chile, and Chimborazo, in Equador, attaining 




Mauna Kp:a, thk Highest Mountain in the Pacific (13,805 feet) 

an elevation of over 20,000 feet. • Mount Vesuvius, the best- 
known volcano of the world, has an altitude of about 4000 
feet, while Mauna Kea, in the Hawaiian Islands, reaches 13,805 
feet. 





Lava Flows on Mauna Loa 
Smooth lava, known as pahoehoe, on the left; granular lava on the right. 

Volcanic Products. — The materials ejected from volcanoes 
are steam and other gases, lava, stones, ash, sand, and dust. 
Of all the vapors given off during an eruption steam is by 



VOLCANIC PRODUCTS 



49 



far the most abundant. This when chilled hovers above the 
vent in the form of a great cloud which upon further conden- 
sation falls as rain. The steam discharge is especially violent 
during an eruption of the explosive type. Steam and other 
volatile substances often escape from fissures and minor vents, 




Lava Cascade, Kilauea 

within the crater, called fimiaroles, as well as from external 
fissures and even from flowing lava. 

Of the volcanic gases the following may be mentioned: hydro- 
chloric acid, sujphureted hydrogen, sulphurous acid, and carbon 
dioxide. 

To the molten product of volcanic action the term lava has 

M.-S. PHYS. GEOG.- — 4 



50 VOLCANOES 

been applied. In its consistency and appearance it is subject 
to a wide range. It may be thin and free flowing when erupted, 
or it may be ropy and viscid ; it may be highly charged with 
steam or other vapor, which expanding imparts a cellular struc- 
ture, or it may be rather compact ; it may be very light colored 
or it maybe very dark — ranging from almost white through 
gray, brown, and even red, to black. In general it has the 
appearance of slag as seen about a smelting furnace. 

An exceedingly cellular form of lava, the consolidated froth, 
forms what is known as pumice or pumice stone. Often lava 
is reduced to fragments so fine as to form dust or ash; or, if 
the particles are coarser, volcanic sand. Again, molten lava, 
of the highly liquid variety, is sometimes, either by the action 
of escaping steam or by the blowing of the wind, drawn out 
into long, deHcate fibers, like spun glass, called by the native 
Hawaiians " Pele's hair" in honor of the goddess of Kilauea. 

Volcanoes Classified. — Volcanoes may be classified as active, 
dormant, or extinct. Active volcanoes eject various substances. 
When no signs of activity are given for a considerable time, the 
volcano is said to be dormant. When a volcano has been dor- 
mant for centuries, and it seems probable that its activity is lost 
forever, it is said to be extinct. 

The frequency of volcanic discharges is varied. Some vol- 
canoes are continuously active. Stromboli has been for 2000 
years in a state of constant but not dangerous activity. It is 
visible at night in every direction for the distance of more than 
100 miles. A red glow is seen frorn time to time above the 
summit of the mountain due to the illumination of the vapor 
cloud by the red-hot lava in the crater. This becomes gradu- 
ally more and more brilliant, and then as gradually dies away. 
It is this phenomenon which has given to Stromboli the name 
" Lighthouse of the Mediterranean." 

On the other hand, Cotopaxi has been in eruption only seven 
times in 100 years. 

Vesuvius exhibits great irregularity. It had been long dormant previous to 
the eruption of a.d. 79, and the steep walls of its crater were covered with 



ERUPTIONS 



51 



vines and other vegetation. Cities and villages graced its slopes. - After this 
eruption, none of great moment occurred until 1631. At that time, one of the 
most destructive on record took place. It continued for three months, and 
destroyed a number of cities and villages. The last eruption occurred in April, 
1906. 

From these and similar facts it is evident that we have no 
knov^ledge of any law which governs the frequency of volcanic 
eruptions. 

Eruptions, — The character of volcanic eruptions is, in a 
great measure, dependent upon the nature of the materials 




Vesuvius in Eruption, April 5, 1906 
A dense column of steam and ashes is rising from the crater. The steam below the sum- 
mit is from a recent lava flow. See also Frontispiece. 

ejected. The emission of great bodies of steam and other gases 
is productive of an eruption of an explosive type, which is usually 
accompanied by a discharge of fragmentary matter of various 
kinds, such as dust, ash, and even blocks of lava. On the other 
hand, when the emission consists mainly of molten lava, the 



52 VOLCANOES 

eruption is less violent, or of the quiet type. Many of the best- 
known volcanoes discharge matter in the gaseous, liquid, and 
solid forms, their eruptions being of a mixed type. 

Eruptions are usually preceded by subterranean rumblings 
and tremors. Before the great eruption of 1872, Vesuvius gave 
indications of unusual activity for a whole year. In many 
cases, however, the eruption follows the warning immediately. 
An eyewitness, writing of Stromboli, says that he had observed 
numerous light, curling wreaths of vapor ascending from the 
crater, then suddenly, without the slightest warning, a sound 
was heard like that of a locomotive giving off steam ; and the 
eruption at once occurred. 

In general, after the preliminary rumblings and tremors, 
dense columns and globular masses of wateiy vapor mingled 
with a variety of gaseous substances issue from the crater. 
According to the state of the atmosphere, and the existence of 
winds and air currents, the vapor assumes a variety of forms. 

In the case of Mount Vesuvius it not unfrequently expands 
after attaining a certain height, and becomes like a vast "um- 
brella," as the Italians call it, having a top many miles in cir- 
cumference. The lurid glare of the boiling lava in the crater 
below is reflected upon the under surface of the umbrella, and 
gives the appearance of a vast conflagration. This spectacle 
is indescribably impressive at night. During a great eruption 
of Vesuvius, vapor, it is said, rose to the height of 20,000 feet, 
or nearly four miles. 

The steam emitted, being condensed, falls as rain. This 
rainfall is excessive and long continued, and often gives rise to 
destructive floods. Around the vapory column vivid lightning 
constantly plays. 

Jets of steam under high pressure, if allowed to issue from an orifice, give 
rise, in doing so, to large quantities of electricity. A machine has been con- 
structed to generate electricity in this way. From it torrents of sparks as 
much as 14 inches in length have been obtained. The crater, with its 
immense volume of uprising vapor, may be compared to a gigantic machine 
of this description. , . - 



ERUPTIONS 



5; 



Often with the vapor are mingled immense quantities of vol- 
canic asJies and sand, which descend and cover the surrounding 
country, sometimes to the depth of many feet. 

Over 1800 years ago (a.d. 79), the cities of Herculaneum 
and Pompeii in Italy were covered with a deluge of ashes 
from an eruption of Vesuvius. They were buried from 70 




Fuji, a Voicwh I'l ak, Japan 
From stereograph copyrighted by Underwood and Underwood. Used by permission. 



to 120 feet, and lost to view for nearly seventeen centuries. 
In 1 71 3, a well digger turned up a bit of statuary, which led to 
the discovery of the two cities. The work of exhuming them is 
still going on. 

The distance to which the ashes of a volcano may be carried is ahiiost 
incredible. In 1845, ^'^^ ashes of Hecla were carried to the Orkney Islands, 
a distance of nearly 700 miles, and in 181 5, those of Tomboro, in the island 
of Sumbawa, fell at Benkulen, iioo miles away. 



54 VOLCANOES 

In August, 1883, during an explosive eruption on the island of Krakatoa, 
situated in the Straits of Sunda, an immense volume of dust amounting to 4} 
cubic miles was suddenly hurled upward into the atmosphere. This great 
dust cloud attained a probable height of 17.000 feet, and so fine were its com- 
ponent particles that they remained suspended for many months in the upper 
air, giving rise, it is thought, to an interesting optical phenomenon known as 
the '' red sunsets." 

During the disastrous outbreak of Mont Pelee, on the 
island of Martinique, in May, 1902, an immense quantity of 
superheated steam and acid vapor charged with incandescent 
lava fragments, in the form of dust, sand, and stones, rolled 
down the mountain side, destroying almost instantly the town 
of Saint Pierre and its 30,000 inhabitants. 

The Emission of Lava in the molten state is the most impos- 
ing of volcanic phenomena. The action which goes on has 
been compared to that which occurs in a pot of boiling por- 
ridge. 

As the mass of porridge is heated, steam is generated at the bottom. This 
rises through the porridge. In doing so it forces a portion upward. More 
and more steam being generated, bubbles of porridge rise to the surface, and 
mimic explosions occur, or the porridge is thrown in little jets above the 
surface of the boiling material. The process may increase in violence until 
the phenomenon of boiling-over takes place. Quite similarly the boiling lava- 
is forced upward higher and higher in its crater by vast volumes of steam that 
are seeking to escape. Explosions occur on the boiling surface, and often jets 
are thrown far into the air. 

Finally, the rising lava overflows the rim of the crater, or quite as often 
bursts through the sides of the mountain, and pours down its slopes in rivers 
of fire. 

So numerous were the fissures which rent Vesuvius in the eruption of 1872 
that liquid lava seemed to ooze from every portion of it, and, as an eye- 
witness expressed it, '' Vesuvius sweated fire." 

Lava streams vary in magnitude. The largest recorded were 
those of Skaptar Jokul, in Iceland, in the years 1783-85. Tor- 
rents of molten rock deluged the island. River courses, ravines, 
and lakes were filled, and the surface of the country for hun- 
dreds of square miles was completely devastated. Some of the 
streams were about 50 miles in length, and in certain places 



DISTRIBUTION OF VOLCANOES 55 

15 miles in breadth, and 100 feet deep. In some of the narrow 
valleys the depth was 600 feet. 

The velocity of the streams, and the distance to which they 
reach, depend on the fluidity of the lava and the slope of the 
land. One thousand feet per hour is a rapid rate ; the extreme 
of 10,000 feet per hour has been observed, though rarely. 

The retention of its heat by a lava stream is very remarkable. 
When the surface of the stream has cooled, it becomes a hard 
crust which prevents the rapid escape of the heat. 

A mass of lava 500 feet thick, ejected from Jorullo in 1759, was seen smok- 
ing by Alexander von Humboldt 45 years after. The Indians lit' cigars at its 
crevices. The lava thrown from Vesuvius in 1858 continued as late as 1873 
to give out steam, and remained so hot that one's hand could not be held in 
some of the fissures for more than a few seconds. 

The flow of the lava is the beginning of the end. After its 
occurrence the showers of ashes gradually cease, the explosions 
become less and less frequent, and at length no evidence of 
volcanic activity remains, save perhaps a vapor cloud veiling the 
summit of the mountain. 

Distribution of Volcanoes. — Two significant facts are to be 
observed regarding the distribution of volcanoes. 

First : The active volcanoes of the globe are, as a rule, situ- 
ated upon areas which are undergoing upheaval. Those por- 
tions of the surface of the earth which are subsiding are without 
volcanic activity. 

Second : Almost all volcanoes are near the sea. Those upon 
the continents are close to the shores. The only well-authen- 
ticated examples of volcanoes situated far inland are those of 
Ararat and Demavend, of Peshan and Turfan, or Hot-Scheou, 
and the Solfatara of Urumtsi, all in Central Asia. 

The most striking exemplification of this law of volcanic distribution is 
presented by the Pacific Ocean. It is literally encircled with active volcanoes. 

There are three great belts traversing the globe, within which 
nearly all the volcanoes of the world are situated. These may 
be called the Pacific Insular Belt, the Atlantic Insular Belt, and 
the American Continental Belt. (See map on p. 57.) 



56 VOLCANOES 

The Pacific Insular Belt. extends along the northern and west- 
ern shores of the Pacific Ocean. Beginning with the Aleutian 
Islands it embraces Kamchatka, the Kurile, Japanese, and Philip- 
pine Islands, Sumatra, Java, New Guinea, the Tonga Islands, 
and New Zealand. 

One extension of this belt embraces the Society,- Marquesas, and Sandwich 
or Hawaiian Islands ; another is the volcanic region of Victoria Land. 

The Atlantic Insular Belt comprises extinct and active vol- 
canoes and volcanic islands which traverse the Atlantic from 
north to south. The islands of Jan Mayen, Iceland, the Azores, 
Cape Verde Islands, Saint Helena, and Tristan da Cunha are 
points which mark this volcanic band. 

The American Continental Belt extends from Cape Horn and 
the South Shetland Islands to Alaska, a distance of more 
than 10,000 miles. All along this line volcanoes, singly or in 
groups, are found. An outlying spur of it includes the Lesser 
Antilles. 

A minor yet very important volcanic belt is that of the Mediterranean 
region. It comprises Etna, Vesuvius, Strom boll, and Vulcano in the Lipari 
Islands, and Santorini and Nisyros in the yEgean Sea. 

Outside of the three great belts there are many volcanoes 
irregularly distributed. In the Pacific all islands not of coral 
origin are composed of volcanic rocks. In the Indian Ocean 
there are volcanoes upon Madagascar and the adjacent islands. 

In central France, in Spain, and generally throughout Europe, 
there are numberless proofs of volcanic action. The volcanoes 
most remarkable for the irregularity of their situation are those 
in Central Asia already mentioned. 

The number of active volcanoes on the surface of the globe 
is estimated at from 300 to 350. Of dormant and extinct about 
1000 are reckoned. 

Volcanoes of the Malay Archipelago. — No other region in the 
world is so thickly studded with volcanic cones as that of the 
Malay Archipelago, of which Java is the center. On that island 
alone they number between 20 and 30. Their discharge, how- 



DISTRIBUTION OF VOLCANOES 



57 




Chart showing the Distribution of Volcanoes 



58 VOLCANOES 

ever, is not usually lava, but sulphurous vapors, acid waters, and 
mud. Occasionally in this region there are eruptions of the 
explosive type on a stupendous scale, as that of Papandayang, 
Java, in 1772, Tomboro, Sumbavva, in 18 15, and on the island of 
Krakatoa in 1883. 

During the famous eruption of Papandayang its cone lost 4000 feet of 
height. Previous to that event it was the loftiest volcano in Java, having an 
altitude of 9000 feet. At the time of the eruption it was thought that this 
great cone had been engulfed and a vast area of land, amounting to 90 square 
miles, swallowed up, including 40 villages. Later investigations have shown 
that the top of the cone was undoubtedly destroyed by an explosion, not dis- 
similar to that of Krakatoa, and that the villages were buried beneath the vast 
mass of dust, sand, and scoria blown from the summit. 

In 1815, Tomboro, on the island of Sumbawa, 200 miles from Java, burst 
forth w'ith such violence that the explosions were heard at the distance of 970 
miles. 

Causes of Volcanic Action. — The fundamental cause of vol- 
canic action is undoubtedly the expansive force of compressed 
steam and other gases. Two cases are conceivable : The com- 
pressed steam and gases may be free, that is, not blended with 
the lava ; or they may be imprisoned within the substance of 
the lava. The force developed will be the same in either case, 
but the mode of action will be different. 

I. TJie action of free gases. — We have already seen that at 
a comparatively shallow depth the earth is intensely hot and 
that water readily finds its way through crevices in rocks or be- 
tween the strata. Should this water, or a portion of it, come in 
contact with heated matter, the effect will be to convert it into 
steam. This may be done with great suddenness. Then con- 
ditions would arise such as cause the explosion of steam boilers. 

A careless engineer allows the water in his boiler to get low, but still keeps 
up the fire. Into the intensely heated boiler he admits water, which is now 
converted into steam with such rapidity and in such quantity that it cannot 
possibly escape. The boiler is unable to resist the pressure, and an explosion 
takes place. 

Water that finds its way into the heated subterranean regions 
of the earth may be suddenly converted into steam. The re- 



CAUSES OF VOLCANIC ACTION 59 

suit is an eruption of the explosive type and the liberation of 
vast quantities of water vapor, dust, sand, and other fragmentary 
products, 

2. TJie action of absoj'bed gases. — The second case, in all 
probability, occurs more commonly than the first, and, in fact, 
seems to offer a possible explanation for most of the phenom- 
ena of a volcanic eruption. 

A number of substances, solid and liquid, absorb, under pres- 
sure and at high temperatures, steam and other gases. Lava is 
one of these. If thus charged the lava in a volcanic conduit 
should be relieved of pressure by the overflow at the vent, its 
capacity for retaining the gases in absorption would be dimin- 
ished. They would expand and force the lava in whatever may 
be the direction of least resistance precisely as the volume of 
gases liberated from gunpowder and similar substances expands 
and forces obstacles before it with explosive violence. 

Among other things this satisfactorily explains the pulveriza- 
tion of lava and the production of volcanic sand and ashes. 
The gases absorbed by the lava being relieved from pressure 
blow it into powder, as wood is blown to pulp for making 
paper. 

Some writers consider tliat volcanoes are due to the shrinkage of the crust 
of the earth compressing and forcing upward molten matter from subterranean 
regions. 

It has also been suggested that the extrusion of the lighter lavas may be 
due to the sinliing of the more condensed or heavier rock above under the 
influence of gravity. This would explain the quiet welling out of lava in some 
volcanic eruptions, especially fissure eruptions. Steam, however, is admitted 
to be the only agency which accounts for the explosive character of eruptions. 



VII. EARTHQUAKES 

An Earthquake is the shaking or trembling of the crust of the 
earth due to the transmission of a jar, shock, or impulse — in the 
form of earth waves — which has its origin below the surface. 
It may be nothing more than a slight tremor similar to that pro- 
duced by the passage of a heavily loaded wagon along the 
street, or it may be a movement of such violence as to over- 
throw and destroy whole cities. 

Earthquakes are usually preceded by a rumbling noise, like 
distant thunder, then the ground rises and falls, houses rock to- 
and fro until they are rent from top to bottom or fall with a crash 
into ruins. In some cases the earth opens with gaping cracks 
which either close again or are permanent. In a few seconds a 
city may be demolished and hundreds of its inhabitants dead or 
dying. 

Earth waves, like sound waves, are elastic waves. From their 
origin, known as the centrum ox focus, they spread through the 
crust in all directions. Although usually regarded as a point, 
the focus is probably, in most instances, 2^. fissure of displacement 
or fault. Its depth below the surface is believed rarely to 
exceed lO or 15 miles, and oftentimes it may be less. 

If the materials of the crust were of the same composition, 
temperature, and density throughout, earth waves would pass 
outward from the focus in spherical shells of alternate compres- 
sion and rarefaction, and the surface zuaves, or visible waves, 
would be the outcroppings of spherical waves which spread in 
circles from a point directly over the centrum, known as the 
epicentrum, as shown in the accompanying diagram. 

There is, however, reason for believing that earth waves are 
ellipsoidal rather than spherical, on account of their accelerated 

60 



DURATION OF EARTHQUAKES 6 1 

velocity in the deeper and more elastic portions of the earth's 
crust, and, further, that the centrum occupies one focus of the 
elHpsoid. 

Owing to the different materials encountered and the vary- 
ing conditions affecting elasticity, an earthquake must be re- 
garded as a very complicated earth movement in which the 




C 
Diagram illustrating the Propagation of Earth Waves 
C, the focus or centrum ; B, the epicenlrum or point on the surface where the shock is verti- 
cal ; A, point on the surface where the shock may be destructive, as here the oscillation 
contains two elements, the horizontal as well as the vertical. It should be noted that, 
if the crust block is homogeneous throughout, the surface waves, which are the out- 
cropping spherical waves, spread in ever increasing circles from the point B. 

waves are subject to many and intricate deviations from their 
theoretical shape, whether spherical or ellipsoidal. 

The velocity of earth waves varies, depending upon the in- 
tensity of the shock, the nature of the media through which 
they pass, and the distance from the centrum, or point of origin. 

The wave velocity of the well-known Charleston earthquake of August, 
1886, was found to be about 190 miles per minute; that of the Japanese 
earthquake of October, 1891, about 78 rniles per minute. Although the speed 
of earth waves is qitite rapid, it varies through a very wide range. 

Duration of Earthquakes. — Earthquakes may be momentary, 
or they may consist of several successive shocks, and these may 
be repeated during long periods. After the earthquake which 
in 1766 destroyed a large portion of the city of Cumana in Vene- 
zuela, shocks were felt nearly every hour for 14 months; and 



62 



EARTHQUAKES 



in Calabria, southern Italy, beginning with the earthquake of 
February, 1783, they were felt for nearly four years. 

In Saint Thomas, also, after the earthquake of 1867, and at 




Diagram illustrating the Ellipsoidal Shape of Earth Waves 

C, the centrum in one focus of the ellipsoid; Z?, the epicentrum. In the passage of the 
waves from the centrum to the epicentrum they would constantly encounter less cohe- 
rent matter and their velocity would be diminished. This is shown by decreasing the 
distance between the waves. In the opposite direction, for reasons stated in the text, 
their velocity would be accelerated. This is shown by increasing the distance between 
the waves. Likewise in other directions the passage of the waves would be affected 
more or less according to the depth below the surface thus producing the ellipsoidal 
shape. 



Charleston after that of 1886, minor shocks were felt for many 
weeks. 

Area of Disturbance. — The area through which the disturb- 
ance extends may be very large. The shock of the earthquake 
of Lisbon, in 1755, was definitely felt as far as Finland in 
one direction, and as far as Madeira in another. 

The disturbance affected the sea to a much greater distance. 
The water rose among the West Indies so that Antigua, 



GREAT SEA-WAVES 



63 



Martinique, Guadeloupe, and Barbados were partly overflowed. 
The area disturbed was four times as large as Europe. 

The Charleston earthquake was the most severe ever experi- 
enced in the eastern part of the United States. Shocks were 
felt from New England to Florida and from the Atlantic coast 
to the middle of the Mississippi Valley. It has been estimated 




VVrkck of a Business Block, California Earthquake of 1906 



that the area of disturbance embraced fully one fourth of the 
entire country, shocks having been felt in no less than 28 
states. 

Great Sea Waves are caused by earthquakes which have their 
center beneath the ocean bed. 

The water at first recedes from the beach, and exposes the 
sea bottom even beyond the usual limits of low water. Then 
the sea wave comes in with a steep front or wall which may be 
50 or 60 feet high. It drives back the receding water, and 



64 EARTHQUAKES 

deluges the shore, sometimes demoHshing whole towns. It 
often passes inland to the distance of several miles. The in- 
habitants, when possible, rush to the hills, and remain there until 
the wave subsides. In many instances the loss of life has been 
appalling. 

The great wave of the Lisbon earthquake was 60 feet high at Cadiz. It 
rose and fell 18 times at Tangier, Africa. 

In 1854, when Simoda, in Japan, was destroyed by an earthquake, the sea 
wave completely overwhelmed the place. The receding wave actually crossed 
the Pacific, and made the water rise on the coast of California. 

Again, in June, 1896, during an earthquake having its center beneath the 
Pacific off the northeastern coast of Hondo,- Japan, the shore of that island 
for the distance of 70 miles was washed by a great sea wave. Many vil- 
lages and towns were destroyed and upward of 30,000 people perished. The 
magnitude of the sea disturbance is shown by the fact that at Honolulu, 3591 
miles away, waves attained a height of eight feet above high water. As in the 
preceding case, the disturbance was registered by proper instruments on the 
coast of California. 

The earthquake at Arica, Peru, in August, 1868, was likewise remarkable 
on account of the size of the accompanying sea waves. Owing to the fact 
that the waves travel faster through the land than through the water, to the 
ruin wrought by earth shocks was added the destruction caused by the inun- 
dation of the sea. 

After the passage of the first earth waves the water receded from the 
shore, then it rose to the height of 30 feet and overflowed the town. Again 
the water receded, and again it rose in a great wave. Then came terrific 
shocks followed by the advance inland of a perpendicular wall of water, from 
42 to 45 feet in height, capped with foam. It rushed over the land, carrying 
with it several ships, among them two naval vessels, which were left stranded 
far from the shore. 

Sea waves are often perceptible throughout an entire ocean basin. They 
travel across the Pacific at the rate of about 350 miles an hour. 

If the center of the earthquake is beneath the land, so near the coast as to 
disturb the sea, the waves produced are thrown out from the shore ajid are 
harmless. This explains why, although the Charleston earthquake was felt 
at sea as far as the Bermudas, no wave damage was done in the harbor of 
Charleston. 

Destructive Effects. — Earthquakes are perhaps the most im- 
pressive manifestations of power in the material world. The 
destruction of life and property occasioned by them is often 



UPHEAVALS AND DEPRESSIONS 65 

enormous. On the ist of November, 1755, Lisbon was shaken 
by the " great earthquake," and in six minutes its palaces were 
in ruins and 60,000 of its inhabitants were dead. 

In March, 18 12, Caracas, in Venezuela, was destroyed, with 
10,000 of its inhabitants. 

Upheavals and Depressions. — Geological changes of great 
importance often accompany earthquakes. 

In the year 18 19 an earthquake occurred in the region ad- 
jacent to the mouth of the Indus. It completely destroyed the 
town of Bhooj, and was felt within a radius of hundreds of 
miles. A tract to which the natives gave the name of " Allah 
Bund," or " Mound of God," was raised where, before, there 
had been a level plain. The " Bund " was 50 miles long, 
16 miles wide, and about 10 feet high. At the same time 
the fort and village of Sindree, with the neighboring region, 
subsided ; the sea flowed into the sunk area, and an inland sea 
was formed covering 2000 square miles. 

During the earthquake at New Madrid, on the Mississippi, 
in 181 1-1812, which covered a period of several months, an area, 
75 or 80 by 30 miles in size, lying west of the town and since 
known as the " sunk country," was permanently submerged. 

Distribution of Earthquakes. — No part of the earth is entirely 
free from earthquakes. In certain parts of Japan tremors 
are felt every day. Vessels not unf requently report earthquake 
shocks at sea. 

In the Old World they are most frequent in a region which 
embraces the northern shores of the Mediterranean Sea, and ex- 
tends eastward into the central portions of Asia. 

In the New World earthquakes are far more common than in 
the Old. Both the eastern and western mountain regions of 
North America are subject to them, but the region of greatest 
frequency is in South America. It comprises Ecuador, Peru, 
and Chile. 

In many places within this region the houses are built of reeds and bamboo, 
lashed by thongs of bulPs hide, and secured in their places with cords instead 
of nails, that they may yield to the shocks without being shaken to pieces. 



66 EARTHQUAKES 

Causes of Earthquakes. — ^Earthquakes have been attributed 
to various causes, such as displacements of the earth's crust, 
slumping, volcanic action, and the collapse of caverns. 

(i) Geologists are of the opinion that in most instances an 
earthquake is due to the formation of a fissure in the crust, and 
that, in the process of readjustment following, one wall sHps or 



Diagram illustrating Faulting of the Earth's Crust 
a, a, b, fault fissure. 

slides over the other with sufficient violence to produce a series 
of jolts or jars. These, transmitted through the adjoining rocks, 
constitute an earthquake. The displacement is known as a fault ; 
earthquakes, therefore, may result from \\\q faulting of tJie crust. 

Faulted rocks are illustrated in the accompanying figure. By the forma- 
tion of the fissure aab and the resulting displacement, the strata on the 
right, or downthrow side, have dropped to a lower level. 

The great California earthquake of April i8, 1906. the severest known on 
the Pacific coast of the United States, was undoubtedly caused by the shifting 
and readjustment of the rocks along an old line of weakness or faulting ex- 
tending from Bolinas Bay, north of the Golden Gate, over the peninsula of 
San Francisco to Salinas and perhaps farther south. 

While the damage resulting from earth movements was very great both in 
San Francisco and the neighboring towns, to the calamity in San Francisco 
was added the tremendous loss of property by fire, which, following the 
collapse of buildings, swept over the entire business portion of the city. 



CAUSES OF EARTHQUAKES 



67 



But if earthquakes are produced by faulting, how is that 
phenomenon to be explained ? It is now believed to be one of 
the results of the cooling and contraction of the interior of the 
earth. As the inner rocks cool and contract, they shrink away 




Fissure of Displacement, Japan Earthquake of 1891 

from the outer layers, some portions of which are left without 
support. Under the pressure of gravity they may now bend or 
they may break. Having broken, they may slide and grind on 
the lower wall of the fissure. The effect upon the senses may 
be faintly illustrated by the jarring and noise produced by a 
heavy body of snow when it slides from the roof of a large 
church. 

By reference to page 86 it will be seen that the above cause furnishes the best 
explanation yet offered not only for the formation of faults and fissures, but 
also for the formation of the great mountain systems of the earth, whether of 
the folded or block type. If this view be correct, then, when mountain mak- 
ing is going on, earthquakes should be of common occurrence. We have 

, M.-S. PHYS. GF.OG. — 5 



68 



EARTHQUAKES 



reason to believe that such was the case in the past, as it undoubtedly is in the 

present. 

(2) There are earthquakes which seem to arise from volcanic 
action, especially that of the explosive type, but tremors of this 
kind affect a much smaller area than the preceding. As to their 

cause, it has been 
suggested that the 
sudden formation and 
explosion of steam 
within a cavity of the 
earth or its rapid con- 
densation accom- 
panied by a collapse 
might account for the 
phenomena, or, in 
other cases, the pene- 
tration of the rocks 
by molten lava. 

Earthquakes are of com- 
mon occurrence in the 
vicinity of the Mediter- 
ranean volcanoes, Vesu- 
vius, Etna, and Stromboli. 
An earthquake of un- 
usual severity occurred on 
the slope of Mauna Loa, 
a Hawaiian volcano, in the 
spring of 1868. For six 
days shock followed shock 
with increasing violence. 
" The ground rolled in 
great waves, rapidly sway- 
ing in every conceivable 
direction, including the 
vertical." The crests of 
the earth waves cracked 
open ; finally a sheet of 
molten lava was projected 
violently skyward. 




Displacement of Railroad Track by Earth- 
quake Fault or Rift. Two Views of the 
Track of the North Shore Railroad at 
Tomales, Marin County, California, after 
the Earthquake of 1906 



CAUSES OF EARTHQUAKES 



69 



(3) In some instances earthquakes of a local character have 
been attributed to the collapse of caverns. In limestone regions 
especially, through the dissolving action of subterranean water, 




Fault Line at Olema, Marin County, California. Typical Appearance 
IN Hard Ground. Earthquake of 1906 

large caves are formed. As they are enlarged their roofs are 
weakened and in places may finally fall. The jar thus produced 
may be sufficient to account for a small earthquake. 

The collapse of Mount Cernans in 1840 has been cited as an example of the 
probable action of underground water. The Jura Mountains are especially 
noted for their large springs. In this particular instance many years before a 
large spring had disappeared which thereafter, by dissolving the underlying 
rock, may have made possible the fall of the mountain. Earthquakes from 
such a cause are not common. 



PART IL — THE LAND 



VIII. THE LAND MASSES 

Relation of Land, Water, and Air. — In the preceding pages 
we have regarded the earth as a whole. In those which are to 
follow we shall consider somewhat in detail those parts of the 
earth which are accessible to man — the solid portion or litJio- 
sphere, the watery portion or hydrosphere, and the aerial portion 
or atmosphere ; we shall also consider the phenomena which 
belong to each and the forms of life which they support. 

Although easily recognized and apparently distinct, the litho- 
sphere, hydrosphere, and atmosphere interpenetrate one another 
in a most remarkable manner, and this interpenetration has a 
most important bearing upon life. Were it not for air in the 
water, fish would perish ; were it not for water in the ground, 
most plants would die and animals starve ; were it not for water 
in the atmosphere, rainfall would cease and desolation reign. 
Further illustrations are unnecessary to show that the land, the 
water, and the air are to be regarded as parts of a great mechan- 
ism "which contributes in a variety of ways to the maintenance 
of plant and animal life. 

Distribution of Land. — Of nearly 197,000,000 square miles 
which embrace the surface of the earth, about 142,000,000 are 
covered by water, and 55,000,000 by land. In other words, 
there is over two and one half times as much water as land. 

The land is found in masses of irregular shape and size, which 
are separated by intervening portions of water. The three 
largest continuous land masses are called Continents. The 
smaller masses of land are called Islands. 

Most of the land is in the northern half of the globe. It 

70 



NORTHERN AND SOUTHERN HEMISPHERES 7 1 

surrounds the North Pole in an almost continuous ring, and 
from the polar regions it extends in long irregular masses 
toward the south. We may consider the great land masses as 
forming three pairs of grand divisijus. The pair comprising 
North America and South America affords the most perfect 
example of this arrangement ; that consisting of Europe and 
Africa is less well defined ; while that is most irregular which 
comprises Asia and Australia. 

In regard to shape the grand divisions follow a general law. 
They spread out broadl}^ toward the north, while toward the 
south they taper to points, or throw out peninsulas. Thus, in 
general, they approach the form of a triangle. This is strik- 
ingly illustrated in the case of Africa and the two Americas. 
Europe and Asia combined form a vast triangle. Australia is 
the only marked exception to the rule. 

Almost all the large peninsulas are southern projections from 
the grand divisions. 

Northern and Southern Hemispheres. — The globe is divided 
by the equator into a Northern and Southern Hemisphere. 
North America, Europe, and Asia, two thirds of Africa, and 
a portion of South America are contained in the Northern ; 
Australia, part of Africa, and the greater part of South America, 
in the Southern. There is three times as much land in the 
Northern as in the Southern Hemisphere. 

The Northern Hemisphere is the seat of knowledge, civiliza- 
tion, and power. It is the commercial hemisphere. 

The Southern Hemisphere has never been the seat of power. 
The Peruvians and the Javanese were the only nations which 
attained a high degree of civilization there. Only about one 
fifteenth of the population of the globe have their home within 
this hemisphere. 

Land and Water Hemispheres. — The earth may be divided 
into two hemispheres, one of which contains nearly all the 
land, and the other nearly all the water. These hemispheres 
are known as the Land Hemisphere and the Water Hemi- 
sphere. London is nearly at the center of the Land Hemi- 



72 THE LAND MASSES 

sphere ; New Zealand nearly at that of the Water Hemisphere. 
Australia presents the largest extent of land in the Water 
Hemisphere. 

Coast Line of the Grand Divisions. — Everywhere the sea more 
or less deeply indents the land. These indentations form navi- 
gable seas or sounds, harbors or roadsteads. The length and 




The Land Hemisphere 

indentation of the coast line, therefore, are indications of the 
commercial capabilities of a grand division. 

Comparing the several grand divisions, we find that the 
southern have far more regular outlines than the northern. 
Their indentations are comparatively limited, and their coast 
line short. The contrast is most marked between Europe and 
Africa. 



COAST LINE OF THE GRAND DIVISIONS 73 

Europe has six times more coast line in proportion to its area 
than Africa. The effect of this has been very important in the 
history of the two grand divisions. By the multitudinous seas, 
bays, and gulfs of Europe intercommunication of one part of the 
grand division with another, and with other portions of the world, 
has been facilitated, and thus its several countries have been 




The Water Hemisphere 

rendered accessible to commerce and civilization. Europe has 
enjoyed among the grand divisions the leadership in commerce. 
Africa, on the other hand, with its comparatively unbroken 
coast line and scanty harbors, has been rendered by nature far 
less open to extensive intercourse with the outside world. 

. North America, though in a less degree than Europe, is 
preeminent for the indentation of its sea coast. This con- 



74 THE LAND MASSES 

tributes to render it the companion of Europe in commerce 
and civilization. 

Coast Lines not Permanent. — In past ages of the earth much 
that is now land was accumulated beneath the sea in the form 
of silt, sand, and limy deposits. From time to time these 
deposits were elevated above the water, forming new land. 
Thus coast lines were changed and the shape of the land 
masses altered. But this was not all. There were movements 
of depression as well as elevation. By the sinking of the land 
rivers were drowned and estuaries formed, and by the subsidence 
of coastal mountains, islands were left as offshore monuments 
of a retreating coast. These are some of the results arising 
from diastropJiic or great earth movements. Even during the 
present time in many places the land has given way before 
the incessant beating of the waves, while in other places the 
shore has been extended by the formation of sand reefs and 
mud flats. So it must have been in the past. The coast lines, 
therefore, are not permanent and the shape of the continents 
has undergone many alterations. There has been, however, an 
upbuilding or evolution of the land from the primitive nuclei to 
the more highly developed areas which now furnish an abiding 
place for man. Yet, notwithstanding these changes, broadly 
speaking, both the land masses and the oceanic basins exhibit 
a high degree of permanency. 



IX. RELIEF OF THE LAND 

General Statement., — The 7'elief of the land is sliown by its 
" physical features," or the irregularities of its surface, such as 
plains, hills, plateaus, mountains, and valleys. Although differ- 
ing greatly in form, they represent, in the main, the combined 
results of two opposing forces: earth movements and erosion. 

By eartJi Diovemcnts reference is made not only to the 
great upheavals by which the continents were elevated, but also 
to the yielding of the earth's crust, through folding and faulting, 
in the formation of mountains. By erosion is meant the wast- 
ing or degrading of the land, chiefly by the action of water, 
whether in the liquid or the solid state. By this action all 
elevations are more or less modified, and in the past plateaus 
and even mountains have been reduced to the condition of low 
plains. 

Relief, therefore, cannot be regarded as permanent. The 
forces concerned may act with great slowness ; but time is long, 
and although the changes wrought are apparently insignificant, 
their ultimate result may be to change completely the physical 
aspect of the land. 

Mean Height of the Land. — The average elevation of the con- 
tinents is not great. It has been estimated that if all the moun- 
tains were leveled, and all the valleys filled up, the land of the 
globe, taken as a whole, would not be raised, on an average, 
much over 2400 feet above the sea. 

Although the mountains are so massive in size, and reach so far toward 
the heavens that their highest peaks can with the greatest difficulty be scaled, 
yet, when compared with the size of the earth, their huge proportions dwindle 
into insignificance. 

A mountain five miles high, which is higher than any but the loftiest peaks 
of the Himalaya or Karakoram, rises above the sea level but g^^ part of the 

75 



76 RELIEF OF THE LAND 

earth's radius. Hence upon a globe i6 inches in diameter, it would be 
represented by an elevation of only j-Jg of an inch, about the thickness of 
three leaves of this book. 

On a globe i6 feet in diameter, the highest mountains would rise above 
the surface less than one eighth of an inch. 

Forms of Relief. — According to their relief, the various forms 
of land are classified as lowlands or highlands. 

Lowland! are usually elevated less than looo feet above the 
sea. They are commonly called plains. 

Highlands have an elevation of lOOO feet or more above the 
sea. They are called plateaus or table-lands and mountains. 
Hills are inferior elevations. They may rise from plains or 
from plateaus ; they may fringe a table-land from which they 
have been separated by erosion ; or they may be piled one 
above another at the base of mountains. In the condition 
last mentioned they are termed foothills. 

Between the various forms of relief sharp distinctions cannot always be 
drawn. Plains, for example, may gradually pass into plateaus, and hills may 
so closely resemble mountains as to be with difficulty separated from them. 

Plains are those portions of the earth's surface which have 
only a moderate elevation above the sea. They may be level, 
rolling, or diversified with hills. When covered with grass and 
generally destitute of trees, they are called prairies in our coun- 
try, pampas or llanos in South America, and steppes in Asia. 
The densely wooded plains of the Amazon are called silvas. 
About one half of the continental surfaces consists of plains. 

For convenience plains may be grouped as follows : coastal 
plains, river and lake plains, and interior plains. It must be 
understood, however, that these groups are not always distinct, 
for one form may imperceptibly blend with another, as is con- 
spicuously shown in the case of the Gulf coastal plain and the 
flood plain of the Mississippi River in several of the Southern 
states. 

Coastal Plains, as their name implies, are those bordering 
coasts. They have been formed beneath the sea and later 
elevated into land. Of this there can be no doubt. The loosely 



COASTAL PLAINS 



77 



compacted strata of sand and gravel, the beds of silt and clay, 
the presence of sea shells and the hard parts of other marine 
animals furnish indisputable evidence. Such plains, lying be- 
tween the highlands and the shore, are in some instances quite 
broad, as along the Atlantic coast of the United States from 
New Jersey southward ; in other instances they are narrozv, 




A Narrow Coastal Plain 

sometimes quite narrow, as shown by the low-lying strips frin- 
ging, in many places, the Pacific coast of both North and South 
America. 

The beds or strata underlying a coastal plain incline or dip 
seaward at a low angle. They are also of varying degrees of 
hardness. As soon as the newly made plain emerges from the 
sea a stripping of its surface begins. The chief agents con- 
cerned in this are rain, running water, and ice, and the process 
as a whole is termed deiiitdation. Streams from the higher 
land now pass down over the plain, excavating shallow chan- 
nels. As the plain rises higher, the stream ways are deepened 
and tributary streams may originate upon its surface. The 
softer the rocks, the more rapid the denudation becomes. If in 



78 



RELIEF OF THE LAND 



time it should happen that where the softer strata outcrop the 
plain is trenched and where the hard strata outcrop there is 
left a belt of upland, presenting a scarp to the interior and a 




A Belted Coastal Plain 
The strata are inclined (dip) seaward. At the base of the upland the plain is trenched. 
Here the weaker strata have yielded to erosion, while the harder strata above form an 
inward-facing scarp. 

seaward slope to the exterior, on account of its belted relief 
such a plain would be termed a belted plain. 

The conditions above described appear in southern New Jersey. Here the 
Delaware River in its lower course flows in the trenched portion of the coastal 
plain. To the southeast the land becomes hilly and passes into an upland 
belt which on its seaward side slopes gradually to the lowland skirting the 
shore. 

River and Lake Plains are often termed alluvial plains. They 
have been formed from materials washed down from hills and 
mountains. In the lower course of a river, where the amount 
of sediment received is greater than the current can urge on- 
ward, the inequalities of the river bed are buried beneath alluvial 
deposits which form a bottom land subject to overflow in times 
of flood. Such an area is known as -ai flood plain. An extension 
of a flood plain into a lake or sea may take place, and if the 
stream is impeded by the accumulated matter, it may discharge 



RIVER AND LAKE PLAINS 



79 



through several mouths, forming a delta. 
delta a delta plain is formed. 



By the growth of a 



The flood plain of the Mississippi River below the mouth of the Ohio, ex- 
clusive of the delta, has an estimated area of 16,000 square miles. Its width, 
between the high banks or 
bluffs, varies from 20 to 80 
miles. The area of the Mis- 
sissippi delta is approximate! \' 
12,300 square miles. The com- 
bined delta of the Ganges and 
Brahmaputra rivers is of ver}- 
great size, some estimates 
reaching 50,000 to 60,000 
square miles. The typical delta, 
shaped like the Greek letter of 
that name, is that of the Nile. 
Its area is about gooo square 
miles. These illustrations serve 
to show the magnitude of 
river deposits. Even where 
true deltas are not formed the 
extension of the coastal plain 
seaward by river action is seen 
in the formation of delta shore 
lines. 

The Nile Valley and that of 
the Menara in Siam are annu- 
ally overflowed, and covered, 
when the flood subsides, with a 
fine sedimentary deposit. This 
consists of rich fertilizing mate- 
rials brought down from distant 
mountain slopes. It imparts 
perennial fertility. It has clothed 
the land of Egypt with verdure 
since the days of the Pharaohs, 
thousands of years ago. It se- 
cures the great rice crop of Siam. 




Delta Shore Lines of the Gulf Coast 
By the deposition of waste, stripped from the higlier 
lands by the Brazos, A, the Colorado, B, and 
the Rio Grande, C, the coastal plain has been 
extended giilfward, giving rise to " delta shore 
lines." I, Galveston ; 2, Matagorda Bay ; 3, Cor- 
pus Christi Bay ; 4, Laguna Madre. 
Attention is also called to the long, sandy, reef-like 
islands inclosing the bays and lagoons. 



Streams emptying into lakes tend to fill them with deposits 
of gravel, sand, and mud, while in smaller bodies of water the 



8o 



RELIEF OF THE LAND 



growth of vegetation is considerable. If above the sea level, 
the outlets of these lakes are gradually lowered by erosion and 
in the course of time they are drained. In this manner many 
lake plains have been formed. In some instances the drainage 
of lakes may not be complete, or the exposure of the lake de- 




TiiE Nile at Flood 

posits may be due to the warping of the earth's crust. In such 
cases the level areas exposed along the shore are also desig- 
nated as lake plains. In some parts of the world, too, lake plains 
have resulted from desiccation, or the drying up of the lake 
waters, due to climatic changes. Where arid conditions still 
prevail, these old lake bottoms now form desert plains. 

Interior or Inland Plains are those lying within the continents. 
More or less inclosed by mountains and drained by large rivers, 
they partake of the general character of valleys, but are on a 
grander scale. Their origin is not due to river action, but rather 
to the great forces of upheaval whereby continents have been 



BASE LEVEL AND PENEPLAINS 8 1 

elevated and mountains formed. Broadly speaking, the surface 
of these plains is rolling or undulating, but many areas of con- 
siderable extent are quite level. The great central plain of 
North America, lying in the basins of the Mississippi and Mac- 
kenzie rivers, and the combined plains of the Orinoco, Amazon, 
and Plata rivers in South America, afford excellent examples of 
this class. 

That portion of the interior plain of the United States lying at the base of 
the Rocky Mountains is known as the " Great Plains." It is treeless, owing to 
the arid conditions prevailing there, and on account of its unusual altitude is 
often classed as a plateau. While its appearance is that of an extended prairie 
region, it should not be confounded with the true prairies lying at a lower 
altitude and nearer the Mississippi River. They are fertile areas of treeless 
land susceptible of high cultivation. 

Base Level and Peneplains. — When a stream has cut its 
channel down to the level of the body of water into which it 
empties, it can excavate its bed no deeper. It has reached its 
lowest point, or base level. Such a stream, if it flows across a 
plain, will now begin to meander, cutting away its banks later- 
ally. As this proceeds, the inequalities of the plain will even- 
tually disappear until the plain itself is base-leveled. 

To indicate a stage preceding that just described, in which 
the divides between the streams may still be recognized as low, 
rounded, but inconspicuous hills and swells, the term peneplain 
(almost a plain) is employed. 

It has frequently happened in geologic time that plains, plateaus, and even 
mountains, by the incessant action of the erosive agents, have been reduced 
to the peneplain or base-level state. 

Plains the Centers of Civilization. — Owing to their fertility 
and ease of cultivation, plains have been, throughout the history 
of man, centers of population, civilization, and power. The 
imperial glory of Nineveh and Babylon, the culture of ancient 
Egypt, the enduring prosperity of China, and the unrivaled 
wealth of India, all owe their origin to the rich soil brought by 
the rivers from the hills. 



82 RELIEF OF THE LAND 

Plateaus or Table-lands are broad, elevated uplands. As 
stated by Gilbert, "they may be indefinitely bounded; they 
may be limited on all sides by cliffs overlooking adjacent areas; 
or descending cliffs may limit on one side and ascending cliffs 
or slopes on the other." The names employed suggest flat- 
ness. Some plateaus, as the Llano Estacado of Texas, are as 
level as the prairies. Generally, however, plateaus present a 
highly diversified surface, hills and even great mountains rising 
from them. 

The plateau of Tibet consists of plains and wide basins, some 
of which contain large lakes, engirdled by ranges of gigantic 
snow-clad mountains. 

The aspect presented also by the great plateau lying between 
the Rocky Mountains and the Sierra Nevada in our own country, 
is that of a vast uplifted mass from which the mountains rise ; 
while the Bolivian plateau, in South America, with the tower- 
ing peaks of the Andes embosoming its upland lake, singularly 
resembles the plateau of Tibet. 

In elevation plateaus vary greatly. Low plateaus, like the 
desert of Sahara, are from looo to 3000 feet in height. The 
loftiest in the world are the plateau of Tibet, 10,000 to 15,000 
feet high, and the BoHvian plateau, averaging about 12,000 
feet. 

Kinds of Plateaus. — According to their origin plateaus may 
be divided into two groups : diastropJiic plateaus, those result- 
ing from the great forces of upheaval ; and vulcanic plateaus, 
those resulting from the outpourings of molten rock or lava. 

Diastrophic plateaus, like the plains bordering the continents, 
have been elevated above the level of the sea. In many 
instances they are composed of stratified rock, sandstones, lime- 
stones, and shales. Oftentimes the strata or layers have suf- 
fered little, if any, displacement, the whole area having been 
lifted bodily. In some regions, however, the rocks have been 
broken, by faulting, into great blocks, now arranged like a series 
of steps, each of which gives rise to a plateau of a different 
altitude. This structure is particularly characteristic of the 



EROSION OF PLATEAUS 



83 



plateaus trenched by the Grand Canyon of the Colorado River 
in Arizona, which have been termed broken plateaus. 




Broken Plateaus 

Part of a section from west to east across the plateaus north of the Grand Canyon of the 

Colorado. From Powell. 

'Vulcanic plateaus have been formed by the cooling of great 
lava floods. In the best-known examples the molten rock 
seems to have welled up through fissures in the crust now com- 
pletely concealed beneath the successive outpourings. 

In the northwestern part of the United States there is a vast 
area, not less than 150,000 square miles in extent, embracing 
portions of northern California, Nevada, Idaho, Oregon, and 
Washington, covered with these surface flows or sheets. Where 
cut by the Columbia River the aggregate thickness of the sheets 
composing this plateau is found to exceed 3000 feet. 

Erosion of Plateaus. — By the action of rain and flowing 
water plateaus are gradually worn away, or eroded. 

Streams originating upon or crossing a recently elevated 
table- land deepen their channels until canyonlike valleys are 
formed. In this manner a plateau is dissected. 

As the stream wear continues, tributaries are extended, canyon 
walls undermined, and valleys broadened. In the meantime the 
intervening land, or ridges, assume somewhat of a mountainous 
aspect, the rather uniform sky line serving in a general way to 
indicate the surface of the former plateau. As stream dissec- 
tion and erosion continue, the ridges become lower and less con- 
spicuous until they finally disappear, save here and there a 

M.-S. PHYS. GEOG. — 6 



84 



RELIEF OF THE LAND 



flat-topped hill, or mesa, capped with a layer of hard, resisting 
rock. The plateau has now reached the zvorn-down stage. 

Plateaus cut by canyon valleys may be classed as young ; 
those well dissected by stream ways, with intervening hills or 
"mountains," as mature ; and the worn-down plateau, as old. 






^- V ^^'«^a.m'--g>^ " j-i \^ ','v*>> f n&v^'\£- • V K'»j 



The Bad Lands of South Dakota 
Illustrating the effects of erosion upon soft rocks in an arid region. Unprotected by vege- 
tation, the valley walls are readily sculptured by water action notwithstanding the 
scanty rainfall. 



Plateaus Unproductive. — The plateau regions of the world 
are for the most part unproductive. Many of them are absolute 
deserts. Hence few plateaus have ever become centers of 
population and power. It is interesting, however, to observe 
that the table-lands of Mexico, Peru, and Tibet have each been 
the seat of a civilization peculiarly its own. 



MOUNTAINS 



!5 



The desert plateaus have undoubtedly their part to perform in the economy 
of nature. They are not wastes in the sense of being wasted or useless areas. 
Their effect upon the rainfall and its distribution is most important. It will 
be more fully considered when we treat of the moisture of the air. 




The Matterhorn, or Mont Cervin 
This celebrated peak has an altitude of 14,705 feet. From stereograph. Used by per- 



Mountains. — The higher and more conspicuous elevations of 
the earth's crust are termed vioiintains. Although they some- 
times stand singly, as Etna or Vesuvius, more often they are 



d,6 



RELIEF OF THE LAND 



joined together in the form of a connected series called a range 
or cJiain. Mountain chains seldom occur solitary. Usually 
two or more are parallel, or nearly so, forming a mountain 
system. Of this the Andes, the Alps, and the Appalachians 
afford striking examples. 

Descriptive Terms. — Isolated summits are z-&S\&d^ peaks. The 
top of a ridge from which there is a descent in opposite direc- 
tions is known as a ci'est. The slopes of a ridge or peak con- 
stitute its flanks. A ridge or group of ridges presenting a 
serrated or notched sky line is called a sierra. Sharp-pointed 
peaks are spoken of as horns, a term especially used in Alpine 
regions. 

The Formation of Mountains. — Mountains have been formed 
in at least four ways : by folding or crumpling, by faulting, 
by vulcanism, and by erosion. 

A B 





A Representation of the Effects of Contraction upon an Outer, Yield- 
ing Spherical Covering 

In A the interior of the sphere, a, is shown before contraction. The coat b fits closely 
upon it. In B the interior of the sphere, a, is shown after contraction. The non- 
shrinliing coat, b, in order to fit upon it is now thrown into folds. The amount of 
contraction is shown by a comparison of the radius in A with that in B. 



(i) The folding process is thought to be a result of contrac- 
tion. The crust of the earth is regarded as a spherical shell 
or coat, now practically cool, surrounding a heated, but cooling 



THE FORMATION OF MOUNTAINS 



87 



and therefore shrinking, interior. Under the influence of grav- 
ity the crust is drawn downward, that is, toward the center of 
the earth, and thus a larger spherical surface is made to fit 
closely upon a smaller. This can be brought about only by 
the folding, crushing, and breaking of the crust. 

Although serious objections have been brought against this 




An Upward Fold of the Earth's Crust (Antjcline), near Hancock, 

Maryland 



theory, the fact remains that many of the most prominent 
mountain systems are composed of folded, crushed, and dis- 
turbed strata, as is well exemplified in the Appalachian and 
Jura Mountains. 

(2) In the region of the Great Basin, between the Sierra 
Nevada and the Rocky Mountains, there is found a type of 
mountain structure due primarily to faulting : long, narrow 
ridges with a cliff, or scarp, on one side and a gentle slope on 
the other. Here it would seem that a great plain had been up- 
heaved in the form of a mighty dome which, owing to tension, 
or stretching, was traversed by numerous cracks or fissures. 



RELIEF OF THE LAND 



Finally, by the collapse of the dome, the long, narrow, parallel 
blocks were displaced or faulted and each became a mountain 
ridge. 

(3) The formation of ordinary vulcanic mountains has already 




Diagrammatic Illustration of Block Mountains 
The tilted blocks are carved into hills and mountains and cut by narrow, canyon-like 
gorges, while the valleys between them are filled with wash, sand and gravel, brought 
down from the adjacent heights. The streams in such a region either are lost in the 
sands or flow into lakes, permanent or temporary. 

been illustrated in the description of volcanoes, the cones of 
which are built up by the ejectment of cinders and ash, the 

outpouring of lava, 
or by both of these 
processes. 

There is, however, 
a type of vulcanic 
mountain of quite a 
different structure. 
Through a fissure, 
or conduit, in the 
earth's crust, not 
reaching the surface, 
molten matter from below has been forced, which, spreading 
out, lifts the overlying strata bodily upward in the form of a 
dome. Later this elevation is eroded or worn away, exposing 




Ideal Section of a Laccolite. 
S, sheets ; D, dikes. 



After Gilbert. 



VALLEYS 



89 



in many places the interior igneous filling, known as a laccolite. 
Such mountains are said to have a laccolitic structure. 

(4) As already stated, dissected plateaus may give rise to a 
rugged country. Here the mountains may be flat-topped, with 
summit scarps or cliffs, and sloping flanks covered with rock 
waste (talus), or they may be rounded off and subdued as in 




The Border of the Edwards Plateau on the Colorado River, West of 

Austin, Texas 



the region of the Allegheny plateau bordering the Appalachian 
Mountains on the west. 

Valleys are depressions through which usually water courses 
run. Every mountain range is intersected by valleys, and every 
mountain system has valleys separating its parallel ranges. The 
valleys intersecting ranges are called transverse. Those lying 
between parallel ranges, and having therefore the same general 
direction, are called loiigititdijiaL 

In regions of folded mountains the formation of valleys is 
largely due to the upheavals and depressions which have dis- 
turbed the surface of the earth. The formation of valleys is 



90 



RELIEF OF THE LAND 




Grand Canyon of the Colorado 



really a part of the process by which mountains are made. 
The action of running water has, of course, widened and 
deepened them. 

Valleys traversing plains and plateaus have been formed by 



GENERAL ELEVATION OF THE LAND 9 1 

the erosive action of water. Of such valleys the most extraor- 
dinary in the world are the canyons of our Western rivers. 

That of the Colorado is a gorge shut in by almost perpendicular walls of 
rock. It is from 3000 to 6000 feet in depth and 300 miles long. Canyons 
are among the most impressive evidences of the age of our earth. Thousands 
of years would be a brief, period for the work of wearing away solid rock by 
running water to the depth of more than a mile as in the case of the Grand 
Canyon of the Colorado. 




A Water Gap 

The Narrows of Wills Mountain, Maryland. Cumberland in tlie foreground. 

From Geological Survey of Maryland. 

The heading together of transverse valleys renders it possible 
to cross lofty mountain ranges. Human ingenuity and indus- 
try have improved these natural courses of travel, or passes, as 
they are called, and some of them have been made marvels of 
engineering skill. The Simplon, Saint Bernard, and Saint Go- 
thard passes, crossing the Alps, are among the most noted. The 
Alpine railroad tunnels have, to a large extent, taken the place 
of the passes. In the eastern portion of the United States the 
narrow transverse valleys, through which streams flow, are 
termed water gaps. 

General Elevation of the Land. — Among the best evidences 
of continental elevation are those furnished by raised sea 



92 



RELIEF OF THE LAND 



beaches, water-worn caves, and terraces now found far above 
the seat of wave action, and by the occurrence, at various 
elevations, of coral reefs and the shells of marine animals 
still adhering to the rocks upon which they grew. 

In some parts of Great Britain (geologically a part of the 
Eurasian continent) raised sea beaches, five or six in number, 

are found at different 
levels up to loo feet, 
and on the Norwe- 
gian coast there are 
numerous ice-cut ter- 
races, which repre- 
sent successive old 
shore lines. Modern 
coral rock has been 
reported by Alexan- 
der Agassiz as occur- 
ring in Peru at the 
height of 30CO feet 
above the sea level, 
and raised coral reefs 
are found in several 
places fringing the 
Red Sea. 

The above are a 
few of the many ex- 
amples that could be 
cited illustrating the 
elevation of the land masses with reference to the sea level. 
General Subsidence of the Land. — In many parts of the 
world there is evidence of the sinking or subsidence of the 
land. This is shown in drowned valleys, estuaries, and fiords, 
and in the submerging of forests as well as of the works of man. 
The sinking of the west coast of Greenland is a familiar 
example. Here the inhabitants fasten their boats to poles or 
piles driven off the shore. After long intervals, by the subsi- 




A Drowned River — Chesapeake Bay 



CAUSES OF RELIEF 93 

dence of the bottom, the poles disappear benea.th the surface 
of the water and must be reset. 

The stumps of cypress trees show submerged forest land on 
the coast of South Carolina and Georgia; and near the head 
of the Bay of Fundy, in Cumberland County, Nova Scotia, the 
stumps of pine and beech trees, still embedded in the soil on 
which they grew, are covered to the depth of 25 to 35 feet at 
high water. 

The coast of New Jersey also may be cited as a region of 




At the Head of Chesapeake Bay 
Elk and Bohemia rivers from Elk Neck. From Geological Survey of Maryland. 

subsidence, the estimated rate being about two feet a century ; 
and the estuaries known as the Hudson River and Chesapeake 
Bay represent the drowning of former river valleys by subsi- 
dence. The fiords of the northern coasts furnish examples 
of the invasion of glaciated valleys by the sea due to crustal 
sinking. 

Causes of Relief. — What force or forces may have caused 
the general elevation of continents we cannot with certainty 
tell. On the principle that like effects are due to like causes 
we should conclude that the elevation of the continents and the 
formation of folded mountains were produced by similar forces ; 
namely, those resulting from interior contraction and consequent 
crustal deformation. Whatever may be our conclusions on this 



94 RELIEF OF THE LAND 

point, it is clear that the forces have been at work for ages, at 
times silently and gently, again with sudden displacements and 
earthquakes, raising some portions of the earth's surface and 
depressing others. 

Effects of Relief. — The elevations of the earth's surface, 
although comparatively insignificant, are to be regarded as im- 




A Norwegian Fiord 

Sor^ord and the village of Odde. From stereograph copyrighted by Underwood and 

Underwood. Used by permission. 

portant regulators of climate. Not many hundred feet added to 
the relief of a country would suffice to alter its physical aspects 
entirely, converting vineyards into pasture lands, or pasture lands 
into regions of perpetual snow. Reverse changes would result 
from a corresponding diminution in the average elevation. 

Again, relief is the great regulator of drainage. If the sur- 
face of the earth had been a dead level, without hills, plateaus, 
and mountains, there would have been no water courses. The 
whole land would have been one broad marsh incapable of 
drainage, and unsuited for human occupation. 



X. RELIEF FORMS OF NORTH AND SOUTH 
AMERICA 

General Features of Continental Relief. — There are certain 
features of relief that belong to all the grand divisions of the 
continents: i. They are bordered by mountains. 2. They are 
traversed in the direction of their greatest length by a great moun- 
tain system. 3. In each there is usually a subordinate mountain 
system. 4. In each there is usually a depressed central area. 

The line of direction taken by the principal mountain system 
is termed the superior or main axis of elevation. This line is 
not, however, in any case centrally placed, as the word axis 
might seem to imply, but far to one side of the grand division, 
v^hich it thus divides into two unequal slopes. The subordinate 
mountain system follows the inferior axis of elevation. 

North America conforms closely to the general principle of 
continental relief. It has a superior and an inferior highland, 
between which there is a rather low, basinlike interior. 

The superior highland is known as the Pacific highland, the 
inferior as the Atlantic highland, and the interior region as the 
great central plain. 

While these three divisions constitute the main features of 
relief, when considered more in detail it will be found that they 
include many topographic forms which give rise to surface 
expressions characteristic of the grand division. 

The Pacific Highland extends from the Isthmus of Panama to 
the Arctic Ocean. Its general course is northwest and south- 
east. Its inner border, facing the interior of the continent, con- 
sists of many mountain ranges with lofty peaks, which are 
collectively known as the Rocky Mountains. Its outer border, 
facing the Pacific Ocean, also consists of mountain ranges, 

95 . 



96 RELIEF FORMS OF NORTH AND SOUTH AMERICA 




The Relief of North America 
The heavy black lines upon this and the following maps represent, in a general way, the 
extent and direction of the mountain chains. The elevations and depressions are indi- 
cated by the buff and green colors. The buff, according to the depth of its tint, repre- 
sents elevations of greater or less altitude. The green indicates lowlands. 



THE ROCKY MOUNTAINS 



97 



chiefly the Sierra Nevada and the Cascade Mountains. Be- 
tween the boundaries here given, within the territory of the 
United States, lies an elevated plateau region, which consists 



15000 SIERRA ^NEVADA 

-10000 
5000 




APPALACMIAN MTS. 



Profile of North America from West to East 

of three physiographic divisions : the Columbia plateau, or 
that drained by the Columbia River; the Great Basin, or that 
with an interior drainage represented by such streams as those 
flowing into the Great' Salt Lake and the Sink of the Humboldt 
River ; and the Colorado plateau, or that drained by the upper 
and middle portions of the Colorado River of the West. 









> '^-^ 










*^^^^^^^ 


W 


/ 






/^'l^Jz 


W 


1 






^"""^^^ 


ft4 


1 




~ 


'^^^^B 


!--^^tis; 


f 






'^^^^1 






1 E. --' ^^E 




Si^^ 


^ 

P,:^ 


_— «i^^^' 


%^^^ 

^^^^c 




m 


1 


Iter ■ >-^''^SK'*&^^ ^ 


m^'W^^m'^mam 



A Rocky Mountain Summit— Pikes Peak . 

The Rocky Mountains exhibit great variation in structure. 
Many of the ranges seem to have resulted from the upheaval 
of the older or crystalHne rocks, shouldering off the stratified 
rocks which now rest upon "their flanks in a highly inclined 



98 



RELIEF FORMS OF NORTH AND SOUTH AMERICA 



position. This is especially true of the ranges facing the Great 
Plains. Mountains have also resulted from crushing, folding, 
and faulting, and the evidence of igneous action is not wanting. 
The magnitude of the Rocky Mountains will be better under- 
stood when it is known that within the state of Colorado alone 
there are 30 or more peaks each having an altitude exceeding 
two and one half miles. 

The whole region of uplift has been cut and carved, worn, 
and remodeled by the action of snow and ice (glaciers), rain. 




Gateway, Garden of the Gods, Colorado 



and flowing water. Thus the present form of these mountains 
has been wrought — the peaks, domes, and ridges. Rising 
above the timber line, the higher, barren, rocky summits, ex- 
posed to the wasting action of the elements, are covered with a 
mantle of coarse fragments — they are rocky mountains in fact 
as well as in name. 

ll\iQ parks and gardens are features worthy of special mention. 
The former are sheltered valleys, surrounded by mountains, 
the best known being North, Middle, South, and San Luis 
parks; the latter are valleys of erosion formed by the wasting 



THE ROCKY MOUNTAINS 



99 



away of the softer portions of the upturned strata on the flanks 
of the mountains, the harder strata forming an inclosing wall. 
The Garden of the Gods, at the foot of Pikes Peak, near Colo- 
rado Springs, and Monument Park furnish excellent examples 
of the effects of erosion on strata of varying degrees of hard- 
ness. 

Within the Dominion of Canada the Rocky Mountains still 
rise as a lofty barrier between the great central plain and the 





Till-. 



OF Sighs — AN Examtle 



)\, Mom aii-,:s i I'm 



Pacific Ocean. Here are found numerous living glaciers spread- 
ing from the snow-clad summits. Being nearer the Pacific, 
these mountains are more bountifully watered than the ranges 
within the United States, and consequently more heavily 
timbered. 

Many large rivers have their sources in the Rocky Mountains. The Missouri 
and Arkansas and their numerous tributaries, together with the Rio Grande, 
represent the Gulf drainage. The Fraser River in Canada, the Columbia, and 
the Colorado have their origin on the west side of the mountains. The latter 
rivers are remarkable for the depth to which they have excavated their chan- 
nels in their course to the sea. Plateaus and even mountains have been 
deeply trenched, forming the most wonderful canyon gorges in the world. 



LOFC 



100 RELIEF FORMS OF NORTH AND SOUTH AMERICA 

The Sierra Nevada and Cascade Ranges form the western but- 
tress of the Pacific highland. The Sierra Nevada Hes within 
the state of California, extending from Mount Shasta, near its 
northern boundary, in a southeastern direction, skirting the 
valleys of the Sacramento and San Joaquin rivers ; the Cascade 
Mountains extend northward from Mount Shasta through the 
states of Oregon and Washington into the Dominion of Canada, 
following a course parallel to the Pacific coast. 

The Sierra Nevada ranges have an interesting history. 
Originally elevated by a crumpling of the earth's crust, they 
were eroded until represented by mountains of very low altitude. 
Later they again became the scene of a great upheaval. Faulted 
and broken into great blocks, their crest was moved farther east- 
ward and the rugged mass left with a steep slope facing the 
east and a rather moderate declivity facing the west. This 
second elevation was accompanied by lava floods which, issuing 
from great rents and fissures, coursed down the mountain sides, 
filling the old river channels. As a consequence of this a 
readjustment of the streams followed and new valleys were 
excavated. 

Between Lake Tahoe and Owens Lake the Sierra Nevada 
attains its greatest altitude, culminating in Mount Whitney. To 
the highest portion of this region the name of HigJi Sierra has 
been given. Here are found numerous living glaciers filling 
depressions or cirques on the north side of high summits. They 
are all of small size and confined to altitudes exceeding 10,000 
feet above the sea level. 

The Cascade Mountains were in the past the seat of extensive 
volcanic action. Of the many beautiful cones which crown 
their summit Mount Hood is probably the most conspicuous. 
The highest peaks, including Mount Shasta, Mount Hood, 
Mount Rainier, Mount Baker, and the Three Sisters, are snow- 
capped and support living glaciers. Here as in other regions 
of high altitude the upraised mass has been deeply dissected. 

The Columbia Plateau is a region of lava floods. The entire 
area between the Rocky and the Cascade Mountains has been 



THE COLUMBIA PLATEAU 



lOI 



literally buried beneath a vast outpouring of igneous matter, 
forming, when cooled, a great lava plain from which, in places, 
old mountain summits rise in islandlike masses. The flowing 
lava by obstructing the stream ways caused the formation of 
many lakes. Later these were drained and their deposits now 
form rich agricultural lands. 

In its course through the lava beds, the Snake River, for 
several hundred miles, has excavated a deep canyon, forming a 




Mt. Hood from Lost Lake. Height 11,225 Feet 



barrier of considerable magnitude. In this gorge there are 
points where the irregularities of the older land surface are en- 
countered ; these have also been deeply eroded by stream wear. 
Near the head of the canyon the river flows over a lava preci- 
pice, forming a magnificent cataract known as Shoshone Falls. 
That this region has not been entirely free from diastrophic 
movements is shown by the Blue Mountains, which have been 
formed by the breaking and upheaval of a portion of the lava 
plain. 

M.-S. PHYS. GEOG. — 7 



I02 RELIEF FORMS OF NORTH AND SOUTH AMERICA 

The lava floods of the Columbia plateau are among the greatest known in 
the history of the earth. They are exceeded only by those of the peninsula 
of India. 

The Great Basin includes a large area lying between the 
Wasatch Mountains and the Sierra Nevada, characterized by 
its interior drainage and wide-spread aridity. Its width, in an 
east-and-west direction, is fully 500 miles and its length 800 
miles. In its northern portion it attains a 'general altitude of 
4000 to 5000 feet, with mountains rising still higher. In its 
southern portions its altitude is greatly reduced, and in Death's 
Valley, in Southern California, it is several hundred feet below 
the sea level. Its surface is diversified. There are large, level 
desert plains as well as mountains and valleys. As has been 
already stated, the crust of the earth has here been profoundly 
fractured and faulted, and the Basin ranges, trending north and 




Section illustrating the Structure of the Basin Ranges. After Russell. 

south, have resulted from the upheaval and tilting of the long, 
narrow blocks. As they now rest they present a precipitous 
front in one direction and slope off gradually in the other. 
The valleys between the mountains have been deeply filled with 
rock waste, which, issuing from the gorges, has spread out in the 
form of wide fans. 

The streams of the Great Basin either end in salt or alkaline 
lakes or are evaporated or absorbed before reaching them. 
During times of storm mountain torrents, upon reaching the 
valleys, owing to their increased volume, spread out, forming 
temporary lakes. These soon evaporate, and there are left mud 
plains, or playas. Such mud deposits are common in many 
parts of Nevada. 

Formerly the amount of precipitation in this region was 
much greater than at present and there existed large lakes now 



THE GREAT BASIN 



103 



extinct. Their old shore Hnes have been traced for many 
miles and their old terraces and delta deposits have been care- 
fully studied. One of these lakes, of which Great Salt Lake is 
a remnant, spread out over a large part of the western half of 
Utah. It has been named Lake Bonneville. Another exten- 
sive lake existed in the northwestern part of Nevada, of which 



^MK] 




Map of Portions of Utah and Nevada showing the Areas formerly 

OCCUPIED BY the EXTINCT LAKES BONNEVILLE AND LAHONTAN 



Pyramid^ Winnemucca, Humboldt, North and South Carson, and 
Walker lakes are remnants. To this inland sea the name of 
Lake Lahontan has been given. 

" The bare mountains reveal their structure ahnost at a glance, and show dis- 
tinctly the many varying tints of their naked rocks. Their richness of color 
is sometimes marvelous, especially when they are composed of the purple 
trachytes, the deep-colored rhyolites. or the many-hued volcanic tuffs so 
common in western Nevada. Not unfrequently a range of volcanic mountains 
will exhibit as many brilliant dyes as are assumed by the New England hills in 
autumn. On the desert valleys the scenery is monotonous in the extreme, 
yet has a desolate grandeur of its own, and at times, especially at sunrise and 
sunset, great richness of color. ... As the sun sinks behind the western peaks 
and the shades of evening grow deeper and deeper on the mountains, every 



104 RELIEF FORMS OF NORTH AND SOUTH AMERICA 

ravine and canyon becomes a fathomless abyss of purple haze, shrouding the 
bases of gorgeous towers and battlements that seem encrusted with a mosaic 
more brilliant and intricate than the work of the Venetian artists." 

— I. C. Russell. 

The Colorado Plateau occupies the region between the Wa- 
satch and the Park Mountains. On the north it is bounded by the 
Uinta range and on the south it extends into Arizona and New 
Mexico. Through it the Colorado River has cut its canyon. 
Here the earth's crust has been extensively faulted, and by the 
upheaval of great blocks, embracing many square miles of area, 
the plateaus have been ■formed. As these blocks have been 
slightly tilted, their upturned edges form scarps or cliffs, which, 
by the erosion of their softer layers or strata, have retreated 
until the plateaus in places resemble a series of steps or ter- 
races. The higher scarps rise a thousand feet or more, and 
some of them follow quite closely the fault lines. That vulcan- 
ism has not been absent is shown by the occurrence of cinder 
cones, laccolitic mountains, and table mountains capped with 
igneous rock. 

The Atlantic Highland comprises the Appalachian mountain 
system and the plateau of Labrador. These extend from Lab- 
rador nearly to the Gulf of Mexico. 

The AppalacJiian Mountains in their northern course consist 
of a number of disconnected groups such as the White Moun- 
tains of New Hampshire, the Green Mountains of Vermont, and 
the Adirondack and Catskill Mountains of New York. To the 
southward they are composed of several well-marked and nearly 
parallel ranges, separated into two belts by the Great Appa- 
lachian valley, a pronounced depression extending from Pennsyl- 
vania to Alabama. The belt lying nearer the coast is composed 
largely of older rocks in the form of gneisses, schists, and 
granites, collectively known as crystalline rocks, while the inner 
belt is made up of stratified rocks, much folded, compressed, 
and overthrust. To have produced such results it is reason- 
able to suppose that the force exerted must have been very 
srreat. 



THE ATLANTIC HIGHLAND 



105 



The Appalachian Mountains also have an interesting history. 
Originally elevated at the close of the Carboniferous or Great 
Coal-making period, they were subsequently much worn and 
eroded until a lowland was formed. Then, at a later period, 
came reelevation with so slight disturbance that many of the old 
streams were able with slight modifications to retain their former 
courses, which now, much deepened, cross many mountain ranges. 




View in the Southern Appalachians 

Richland Valley from Junakiska Mountain, North Carolina. From United States Geo- 
logical Survey. 

Such is notably the case with the Susquehanna, Potomac, James, 
and New rivers. In the meantime the tributaries of these 
streams have been very active removing the softer and more 
soluble rocks, thus leaving the harder rocks in relief. In this 
manner, rather than by folding, the existing ridges have been 
produced. 

The general elevation of the Appalachians is about 3000 feet 
above the sea, but the culminating points, Mount Mitchell, in 
North Carolina, and Mount Washington, in New Hampshire, 
are over 6000 feet his-h.^ 



1 Mount Mitchell, 671 1 feet; Mount Washington, 6279 feet. 



I06 RELIEF FORMS OF NORTH AND SOUTH AMERICA 




The Relief of South America 



THE CENTRAL PLAIN 10/ 

Toward the interior the Appalachians are bordered by more 
or less dissected uplands known as the Allegheny plateau; on 
the seaward side they descend to the gentle undulating Piedmont 
belt, which, south of New England, is followed by a rather broad 
coastal plain. 

The Central Plain extends from the Gulf of Mexico to the Arc- 
tic Ocean. The Height of Land, a low east-and-west ridge near 
the northern boundary of the United States, divides it into two 
parts. The drainage of the northern portion is to the Arctic Ocean 
and Hudson Bay ; that of the southern portion is to the Gulf of 
Mexico. As the streams of the latter part are mainly tributary 
to the Mississippi River, it is usually known as the Mississippi 
basin. - 

The Mississippi basin bears a strilcing resemblance to a coastal plain. It 
occupies the site of an ancient interior sea. As the crust here has never 
suffered serious disturbance, there is a complete absence of the more strilcing 
features of relief. As far south as the mouth of the Ohio River this region has 
been subjected to glacial action (see page 268). The soils are deep and very 
fertile. They have originated in part from materials transported by glaciers, 
in part from stream and la]<e deposits, and in part from the wasting of rocks 
due to weathering. In the middle West there are large areas of prairie land, 
some exceedingly level, otliers rolling. On the east the prairies merge with 
the wooded region as they approach the Allegheny plateau, and on the west 
they pass imperceptibly into the higher or Great Plains region. Along prairie 
streams there is usually a rather luxuriant growth of trees and vines. 

South America. — The general features of relief as exhibited 
by South America are similar to those of North America. 
There is a superior or Pacific highland and an inferior or At- 
lantic highland, with low central plains between them. 

The Pacific highland includes the Andes Mountains, with their 
long, high valleys, and the lofty Bolivian plateau. The Atlan- 
tic highland, severed by the valley of the Amazon, includes the 
Guiana and Brazilian highlands. 

By many the Andes are regarded as the direct continuation of the Pacific 
highland of North America, which, in crossing the Isthmus of Panama, is 
reduced to a series of rather low hills. 



I08 RELIEF FORMS OF NORTH AND SOUTH AMERICA 

While such close relationship cannot be established between the Atlantic 
highlands of the two grand divisions, each includes in its make-up crystalline 
and the older stratified rocks. 

The Andes are remarkable for their great length, equal to one 
sixth of the earth's circumference, for their height, and for their 
regularity of form. South of Aconcagua these mountains con- 
sist of a single chain, the highlands of the coast being separated 
from them by a broad valley. Farther south, owing to subsi- 
dence, the higher parts of the western ridges appear as islands 
and peninsulas. Between 27° south latitude and the equator 
parallel. eastern and western ranges inclose valleys and plateaus, 




BRAZILIAN HIGHLAND 



Profile of South America from West to East 

wonderful in height and extent, separated by transverse ranges 
or momitain knots. Of the table-lands, the Bolivian plateau is 
broadest and highest, and, like the Great Basin of North Amer- 
ica, has an interior drainage. Upon it is situated Titicaca, the 
largest lake in South America and the highest in the western 
hemisphere. 

North of the Desert of Atacama to the center of Colombia 
this great mountain system is crowned with hundreds of snow- 
capped peaks and studded with smoking volcanoes. For 
the entire distance there is not a mountain pass or gap below 
12,000 feet in altitude, while the loftiest peaks exceed 19,000 
feet, — Chimborazo, 20,498; Cotopaxi, 19,613; Antisana, 19,335; 
and Cayambe, 19,186 feet. 

The northern portion of the Andes consists of three or four 
ranges separated by deep valleys occupied by the Magdalena 
River and its tributaries, which drain into the Caribbean Sea. The 
westernmost range, decreasing in height, blends with the Panama 
hills. 



THE ATLANTIC HIGHLANDS 



109 



Very important in its bearing upon the physical geography of 
the continent is the singular proximity of the Andes to the west- 
ern coast. Their greatest distance from it scarcely exceeds 100 
miles. 





ClIIMUOIiAZO 

This magnificent Andean peak rising above the valley of Quito attains the height of 20,498 

feet above the sea. 



The Atlantic Highlands of South America are those of Brazil 
and Guiana. 

The Brazilian Highland is a broad plateau region traversed 
by nearly parallel ranges Qf moderate elevation. Their loftiest 
peaks are from 5000 to 10,000 feet high. 

Rising above the sea on one side and above the plains on the 
other sides, this great triangular area, embracing 700,000 square 
miles, has been termed the " Brazilian Island." 

Its drainage is mainly inland, to the Amazon and Plata 



no RELIEF FORMS OF NORTH AND SOUTH AMERICA 

systems. Only one important river, the San Francisco, flows 
directly into the Atlantic, and then only after a course of a thou- 
sand miles behind mountain barriers. 

The Highland of Guiana is, a plateau supporting several closely 
set ridges, the most important of which are the Parime Mountains. 
Maravaca, the culminating peak, is nearly 10,000 feet high. 

The Central Region of South America, like that of North 
America, is a well-marked depression lying between the superior 
and inferior highlands. It is called the Great Central Plain. It 
consists of the river basins of the Orinoco, the Amazon, and the 
Plata. These are divided by ridges so low and so narrow that 
the three together may not unfairly be considered as forming 
one great basin. 

The following curious facts will show how nearly alike their level actually 
is. The Cassiquiare, which rises between the Amazon and the Orinoco, forks, 
after running some distance, and sends off one branch to the south to unite 
with the waters of the Amazon, the other to unite with those of the Orinoco 
on the north ; it thus connects these two river basins by a water way that 
permits the Indians to pass in their canoes from either of the two great rivers 
into the other. 

Furthermore, in the Brazilian province of Matto Grosso there are two 
springs side by side, and within a few feet of each other. From one the water 
flows into the y^mazon, from the other into the Plata; and so close are the 
navigable waters of these rivers to each other, that, with a single portage of a 
few miles, the voyager, ascending the Plata from the sea, may return to the 
ocean again, either through the Amazon or the Orinoco. 

Silvas of the Amazon. — The valley of the Amazon is not only 
of great extent, but it is very level. Lying within the tropical 
rain belt, it is one of the best watered regions of the world. This, 
together with the warm climate and rich alluvial soil, has been 
productive of remarkably dense forest growths known as silvas. 
So close together are the trunks of the trees and so great the 
tangle of vines that were it not for the water ways this region 
would be quite impenetrable, as paths are cut with difficulty. 
During the rainy seasons the lower portions of the valley are 
flooded far and wide and the waters even flow through the tree 
tops. On the other hand, during the dry seasons the waters so 



LLANOS 1 1 1 

far recede as to leave strips of meadow land exposed, their long 
submergence having effectually checked the forest growth. 

Llanos. — West of the Guiana highland the low valley of the 
Amazon passes imperceptibly into that of the Orinoco, and 
the forest growth, so characteristic of the former, soon gives 
way to a treeless or prairie region. During the wet or rainy 
season these plains are more or less flooded, but later, when 
the water recedes, they are covered with a luxuriant growth of 
coarse grass resembling great meadows, hence the name llanos 
which has been applied to them. During the dry season, how- 
ever, they present a very different aspect : The Orinoco no longer 
fills its banks, but, miich shrunken, courses its way seaward; the 
grasses and other vegetation have withered away ; the once 
green plains have taken on a parched and desertlike appear- 
ance ; and the smaller streams have ceased to flow. 

The Chaco and Pampas. — The third of the great South 
American basins is that of the Plata. Lying south of the 
Amazonian basin, it is separated from it by a low and almost 
imperceptible divide. Its northern portion is wooded and in 
its forests and swamps are found both wild animals and In- 
dians. Famous as a hunting ground, this region is known as 
TJie Chaco. Roughly located it hes west of the Paraguay River 
and north of the Pilcomayo. 

The larger part of the basin, however, is in the form of 
almost level plains, although occasionally relieved by hills and 
low mountains. They are the pampas. The higher plains 
vary in altitude from 3000 to 600 or 700 feet. They are 
bordered along the Plata and the Parana by low alluvial 
plains. 

The pampas vary somewhat in their surface features. In 
the south they are barren and sandy ; north and west of the 
Cordoba Hills there are numerous saline basins, and in the 
region of Buenos Aires there are rich farming lands. Not- 
withstanding the widespread barrenness, much of the country 
is covered with nutritious grasses, so that the pampas of Argen- 
tina rank among the greatest grazing lands of the world. 




(112) 



-^The Relief oi 




URASIAj, 



("3) 



XL RELIEF FORMS OF EUROPE, ASIA, 
AFRICA, AND AUSTRALIA 

Europe, like North and South America, has its superior and 
inferior highlands and its low plain, but the arrangement of 
these features differs from that prevailing in the New World 
in two well-marked particulars: (i) the main axis of elevation 
extends east and west, not north and south, as in the case of 
the Rocky Mountains and the Andes; (2) the mountain chains 
do not exhibit the characteristic parallehsm shown by those of 
the New World. 

The Superior Highland of Europe stretches across the south- 
ern portion of the grand division, from the Atlantic to the Black 



Alps 




Profile of Europe from South to North 

Sea, and, if we regard the Caucasus as its eastern prolonga- 
tion, it reaches the shores of the Caspian. 

Beginning with the Pyrenees, its western termination, it 
culminates in the Alps. Eastward of the Alps it divides 
into two important branches, a northern, consisting of the Car- 
pathian Mountains, and a southern, consisting of the Dinaric 
Alps and the Balkans. These ranges inclose the Danube 
basin. In addition, the Apennines of Italy and the moun- 
tains of Greece are included in this system. 

The Alps, which cover an area of about 90,000 square miles, 
are the most celebrated of all the mountain systems in the world. 
Their historic and poetical associations, the grandeur and beauty 

114 



THE ALPS 



115 



of their varied scenery, the number and extent of their glaciers, 
and their accessibihty to travelers invest them with an interest 
unrivaled by the loftiest summits of other lands. 

Occupying a central position between France and Germany 
on the north, and Italy on the south, they can be reached in a 
few hours from any of the great cities of Europe. Owing to 




1 HE JUMGi'KAU FROM WENGERNALP 

This snow-clad Swiss summit is a most imposing sight. Its altitude is 13,760 feet. Dur- 
ing the summer months avalanches of ice are of common occurrence, falling from the 
heights into the deep valley beyond the line of trees in the foreground. 

their varied attractions they are visited by so many thousands 
annually, that they have been called, not inappropriately, " the 
playground of Europe." 

^'As we climb the Alps," says a distinguished scientific writer, " peak rises 
behind peak, crest above crest, with infinite variety of outline, and with a wild 
grandeur which often suggests the tossing and foaming breakers of a stormy 
ocean. Over all the scene, if the air be calm, there broods a stillness which 
makes the majesty of the mountains yet more impressive. No huin of bee or 



Il6 RELIEF FORMS OF EUROPE 

twitter of bird is heard so high. No brook or waterfall exists amid those 
snowy heights. The usual sounds of the lower ground have ceased. Now 
and then a muttering like distant thunder may be caught, as some loosened 
mass of snow or ice falls with a crash into the valleys ; or the wind brings up 
from below in fitful gusts the murmur of the streams which wander down the 
distant valleys." 

The highest peaks of the Alpine system are Mont Blanc, 
15,730 feet; Monte Rosa, 15,217 feet; and the Matterhorn, 
14,705 feet. 

The Pyrenees, which extend for a distance of about 250 miles 
•from the Mediterranean to the Bay of Biscay, present a much 
greater uniformity of arrangement than the Alps. Their average 
height (8000 feet) is not greatly inferior to that of the Alps 
(8000 to 9000 feet); but their highest peak, Mount Maladetta, 
11,168 feet, is far below the towering masses of Mont Blanc and 
Monte Rosa. The passes of the Pyrenees, however, are higher 
and less practicable than those of the Alps. 

The Carpathian and Balkan Mountains. — The Carpathians 
separate the plains of Hungary from the great low plain of the 
continent. Their greatest elevation is about 9000 feet. 

Through the southwestern extension of these mountains, known 
as the TransylVanian Alps, the Danube River has cut a long and 
picturese]ue passage obstructed by numerous rocky ledges, the 
chief of which, _ the Iron Gate, is nearly a mile in width. The 
former dangers to navigation at this point have been removed 
by the construction of a canal. 

South of the Iron Gate the mountain barrier merges with the 
Balkans, which, becoming an east-and-west range, is terminated 
by the Black Sea. The highest summits of these mountains do 
not exceed 7000 feet. 

The Caucasus range resembles the Pyrenees in that it lies be- 
tween two large bodies of water, the Caspian and the Black seas, 
and in the further fact that it is well defined. On the north are 
the great Russian plains and on the south the river Kur. The 
length of these mountains is about 700 miles and their width 
varies betv/een 70 and 120 miles. Mount Elburz(i8,526 feet), the 



PENINSULAS I I 7 

most conspicuous peak, exceeds Mont Blanc in height, and the 
entire range is high, with a snow-clad crest and glaciers. This 
great mountain barrier forms a part of the boundary between 
Europe and Asia. 

Peninsulas. — High Europe throws out three mountainous 
projections toward the south : the Iberian or Spanish Peninsula 
on the west, the Italian in the center, and the Grecian on the 
east. 

The Iberian or Spanish Peninsula is a great plateau surmounted by several 
parallel ranges. The Pyrenees, which are the principal of these, form the 
dividing line between France and Spain. 

In the Italian Peninsula we find the Apennines, an important prolongation 
of the Alpine system. These are more famed for their beauty than for their 
altitude. The volcanoes of Vesuvius, Etna, and the Lipari Islands are consid- 
ered as belonging to this chain. 

The Grecian Peninsula, like the Italian, boasts of no very elevated ranges. 
Its mountains are famed less for their height than for their historic and poetic 
associations. They were the mythic homes of the gods of ancient Greece. The 
throne of Jupiter rested on Mount Olympus. The Balkans are the most 
important range. They have an average elevation of about 5000 feet. 

The Inferior Highlands comprise the ranges of Scandinavia 
and the Ural Mountains. 

The Scandinavian mountains consist, for the most part, of a 
broadly elevated region along the western coast of the penin- 
sula. Formerly these mountains were much higher than now 
and indented by many deep valleys. By subsidence these val- 
leys have in their lower portions become arms of the sea known 
as fiords. As they afford safe anchorage and often extend far 
inland, sometimes even a hundred miles, they are commercially 
of great value. On such bodies of water many seaports have 
been established. 

The Scandinavian highlands terminate in North Cape, a great 
bluff, nearly a thousand feet in height, facing the Arctic Ocean. 
This point is visited annually by many tourists for the purpose 
of beholding the "midnight sun." 

The Ural Mountains form a natural boundary between Eu- 
rope and Asia. They extend southward, along the meridian 



ii8 



RELIEF FORMS OF EUROPE 



of 60° east 1500 miles, from the Arctic Ocean nearly to the 
Caspian Sea. 

Low Europe consists of a vast plain lying northeast of the 
superior highland. It is bordered on the northwest by the 
mountains of Scandinavia, and on the northeast by the Ural 





North Cape from the West 
From stereograph copyrighted by Underwood and Underwood. Used by permission. 

range. It extends from the Arctic Ocean to the Black Sea, 
and westward as far as the Bay of Biscay. 

The Valdai Hills, having an altitude of about a thousand feet, 
mark the highest point of a swell which separates the rivers 
flowing into the Baltic and White seas from those which enter 
the Black and Caspian. 



THE SUPERIOR HIGHLAND OF ASIA II9 

The range of this plain in latitude is so great and, as a direct consequence, 
its climate so varied, that it presents several well-marked aspects. The 
northern portion is treeless and of the general character of the lands border- 
ing the Arctic coasts in both hemispheres. P'arther south forest lands appear, 
which still farther south give way to rich prairie lands excepting in regions 
bordering the Caspian, where saline conditions prevail. 

The Superior Highland of Asia consists of two portions : 
(i) the various mountain chains which radiate from the central 
elevated region known as the plateau of Pamir ; and (2) the 
plateau of Tibet. 

The Pamir is called by the Asiatics the " roof of the world." 
In shape it may be regarded as an irregular square. From 
three of its corners great chains project. The southeast corner 
is the starting point of the great ridges of the Himalaya, the 
Karakoram, and Kuen-Lun. From the northeastern corner the 
Thian Shan range takes its origin. From the southwestern 
starts the line of the Hindu Kush. 

The plateau of Tibet lies between the Himalayas on the 
south and the Kuen-Lun Mountains on the north. It is the 
loftiest table-land in the world, having an extreme elevation of 
about 15,000 feet. 



HIMALAYA MTS 




Profile of Asia from South to North 

The Himalayan Range stretches eastward from the Pamir in 
an unbroken course for a distance of 1500 miles. Its breadth 
varies from 150 to 350 miles, and its mean height has been esti- 
mated at 6000 feet higher than that of the Andes. Over 40 
of its peaks rise to an altitude of 23,000 feet, and more than 
70 reach 20,000 feet. Mount Everest, with an elevation of 
29,000 feet, is, so far as known, the highest mountain on the 
fflobe. 



I20 RELIEF FORMS OF ASIA 

The Himalayas present the grandest possible mountain scenery; deep 
gorges wrapt in perpetual twilight gloom ; frightful precipices ; somber for- 
ests of rhododendrons and pine trees ; higher up, vast glaciers filling the 
ravines, and ice and snow covering the ridges which rise one above another 
to such sublime heights as must ever secure their summits immaculate from 
the footsteps of man. Everything is colossal ; but the Himalayas lack the 
smiling valleys and sheltered lakes which impart such picturesque charm to 
the Alps. They possess the grandeur without the amenity, the magnificence 
without the variety, which mark the less elevated European system. 

The passes of the Himalayas, instead of leading through low gaps and 
over gentle declivities, rise up into the regions of perpetual snow and ice, 
and are so difficult as to be of little avail for the purposes of commerce be- 
tween the people on the opposite sides. They are on an average 10,000 feet 
higher than those of the Alps, and nearly 4000 feet higher than those of the 
Andes. We cannot be surprised that India and Siberia are practically farther 
removed from each other than if they were separated by an ocean, nor even 
that the opposite slopes of the Himalayas are occupied by men of different 
races . 

The Karakoram, Kuen-Lun, and Thian Shan Mountains. — The 

Karakoram range traverses the plateau of Tibet, and is supposed 
to have a greater average height than even the Himalayas. It 
contains Mount Godwin- Austen (height, 28,278 feet), believed to 
be the highest summit next to Mount Everest in the world. 

The Kuen-Lun range separates Tibet and eastern Turkestan, 
and is prolonged by the Chinese range of the Pe-Ling Mountains. 

The Thian Shan range forms the northern boundary of the 
plateau of eastern Turkestan. Some of its peaks attain the 
height of 20,000 feet. 

The Hindu Kush extends in broad, massive ranges westward 
for 400 or 500 miles. A depression then occurs. The range, 
however, is really continued in the Elburz Mountains, which 
form the northern boundary of Persia. 

The general direction of the great mountain chains of the 
superior highland region is east and west. 

The Inferior Highlands comprise the Altai Mountains and 
their northern continuations, together with the Great Khin-Gan 
range, and the ranges of southeastern Asia, and, finally, the 
subordinate plateaus of the grand division. 



THE ALTAI AND THE KHIN-GAN MOUNTAINS 121 

The Altai and the Khin-Gan Mountains. — The Altai Moun- 
tains extend in a northeasterly direction, and terminate in 
the Yablonoi and Stanovoi ranges. They separate the desert 
wastes of Mongolia from the plains of Siberia. Some of their 
peaks are 12,000 feet high. 

"Although far less extensive and elevated than the Thian Shan, the Altai 
still bears comparison with the European Alps, if not in the height of its peaks, 
diversity of its forms, abundance of its snow or rich vegetation, at least in the 
development of its ranges and the length of its valleys." — Reclus. 

The Khin-Gan Mountains, with their southern offshoots, form 
the eastern barrier of the great Desert of Gobi. 

The Plateaus of Asia are a prominent feature of the grand divi- 
sion. They extend in a series from the shores of the Red Sea 
nearly to the Pacific Ocean. In general they are arid and rainless, 
sandy, stony, and barren. In the spring their surface is thinly 
sprinkled here and there with grass and herbs, but in the sum- 
mer and autumn it is, for the most part, dry and sterile. 

The sheltered valleys are, however, in many cases exceed- 
ingly fertile. In such valleys there is a settled population, but 
outside of them the plateau region may be described as the 
home of roving herdsmen and marauding Bedouin. 

North of the Kuen-Lun Mountains are two plateaus, eastern Turkestan and 
the Desert of Gobi. These are shut in on the north by the Thian Shan and 
Altai Mountains. The average elevation of eastern Turkestan is about 2000 
feet above the sea level ; that of Gobi, about 4000 feet. Entering Gobi from 
Tibet, we should descend fully 9000 feet. 

The triangular plateau of the Deccan in India rises to the average height 
of about 3000 feet. The sides of the triangle are the eastern Ghats, the 
western Ghats, and on the north the Vindhya Mountains. 

^The plateau of Iran or Persia, including large portions of Afghanistan and 
Baluchistan, is shut in by the Elburz and Hindu Kush Mountains on the north, 
by the Zagros chain on the south, and the Sulaiman on the east. It rises from 
3000 to 4000 feet above the sea level. 

The plateau of Armenia, with Ararat (about 17,160 feet high) for its culmin- 
ating point, rises to the westward of Persia. 

The plateau of Asia Minor lies westward of that of Armenia. It has an 
average elevation of 2500 feet. The Taurus ranges bound it on the south. 

The plateau of Arabia forms the southwestern projection of Asia. 



122 



RELIEF FORMS OF ASIA 



The Great Lowland of Asia lies to the north. It extends 
from the shores of the Arctic Ocean southward to the base of 
the Altai Mountains and the adjacent ranges, and comprises the 
Kirghiz Steppes and the Siberian Plain. 

It is a part of the almost continuous depression which extends through 
Europe and Asia, from the North Sea to Bering Strait, a distance of more 
than 5000 miles. 

The Kirghiz Steppes are wide and monotonous tracts, covered 
in spring with rough grass, parched with drought in summer, 
and bleak and desolate in winter. 




The Dead Sea, Palestine 
This remarkable salt-water lake occupies the deepest known depression of the land below 
sea level. Its length is 47 miles ; its greatest width does not exceed 10 miles ; its sur- 
face is 1292 feet below that of the Mediterranean Sea ; and its greatest depth is 1310 
feet. From the eastern and western margins of the sea the land rises precipitously 
in the form of great limestone cliffs. 

The Siberian Plain consists of prairies and piny forests in its 
southern portions ; of swampy tundras on its northern edges. 



THE GRAND DIVISION OF AFRICA 1 23 

Inferior in size to the Siberian Plain, but vastly more impor- 
tant for their influence upon the history of the human race, are 
the plains of China and India. They support nearly one half 
the population of the globe. 

Two remarkable depressions are found on this grand division. 
One is occupied by the Dead Sea, the surface of which is 1300 
feet below the level of the ocean ; the other by the Caspian, the 
surface of which is 84 feet below. 

The Grand Division of Africa obeys less closely the general 
law of continental relief. It has, however, mountain ranges along 
the coast, while a plateau region of less elevation occupies the 
interior. Its superior^ highland, lying on the east, is broken by 
rivers into pronounced segments. Notwithstanding that its 
mean elevation is said to exceed that of Europe and even Asia, 
its mountains can scarcely be compared with the Alps in magni- 
tude, much less with the Himalayas. 

The Superior Highland consists of an elevated region which 
extends from the Isthmus of Suez to the Cape of Good Hope. 
One important portion of it, the plateau of Abyssinia, attains 
an elevation of 7000 to 8000 feet. The culminating points, 
however, are the snowy heights of Kenia, KiHmanjaro, and the 
Ruwenzori Mountains (about 19,000 feet), near the equator. 
South of these elevations occur the Livingstone Mountains 
(5000 to 10,000 feet), walling in Lake Nyassa; and nearly at the 
southern extremity of the continent lie the Snow Mountains, 
which may be considered as vast terraces ascending from the 
sea toward the interior. 

The plateau of Abyssinia has been described as a " block " of the older 
crystalline rocks, gneisses, and schists, capped with lava sheets. Its surface 
has been profoundly eroded, and in places the accumulation of volcanic matter 
is said to form high mountains. Lake Dembea occupies a depression 3000 
feet below the general level and is regarded as the chief source of the Blue 
Nile. 

The Inferior Highlands include the ranges which border the 
northern and western coasts. The Atlas Mountains on the 
north consist of three or four parallel ranges which ascend from 



124 



RELIEF FORMS OF AFRICA 




The Relief of Africa 

the Mediterranean stage by stage, and increase in height to the 
westward. 

The Kameruns and the mountains near the headwaters of the 
Niger are the principal elevations on the west. The Kameruns 
are volcanic. They attain at some points the height of nearly 
13,000 feet. 



THE INTERIOR 



125 



The Interior of the grand division may be regarded as a vast 
plateau bordered by the various coast ranges. Low plains are 
to be found only along the coast. 




A Caravan on the Desert of Sahara 

The plateau region may be divided into two sections: (i) 
that portion which consists of prairies and fertile river basins ; 
and (2) the arid Sahara. 

The Sahara stretches east and west 3000 miles, north and south 




Inspiration Point, Blue Mountains, New South Wales, Al^ikmiv 
Photographed by Sterling Fulmore. 

1000, covering an area of 2^ millions of square miles. It is not 
an absolute level. Its average elevation is about 1200 feet, but 
it contains areas which are 4000 or 5000 feet in height, and 
has a mountain range one of whose peaks is nearly 8000 feet 



126 



RELIEF FORMS OF AUSTRALIA 




The Relief of Australia 



high. Southward of Tunis are found depressions, some of 
which are lOO feet below sea level. They are marshy regions 
for most of the year, but when the winter rains fall they receive 
the drainage from the mountains, and thus become broad, open 
lakes known as chottes {shots). The surface of the desert con- 
sists, in some places, of sharp stones, in others of gravel, in 
others again of shifting sand. The latter when driven before 
the wind is arranged in long, huge billows called dunes. 

Here and there over the desert are found fertile spots or oases 
where water may be obtained either from springs or wells. 

Australia somewhat resembles Africa in its relief. It has an 
elevated border and a depressed interior. 

The superior highland lies along the eastern and southeastern 
shores. It includes the Blue Mountains and the Australian 



AUSTRALIA 12/ 

Alps, culminating in the latter, the loftiest peaks of which are 
about 7000 feet high. 

The inferior highland borders the western and northwestern 
portions of the continent. 

Of the central lowland the basins of the Darling and Murray 
rivers are best known. Of the remainder much is desertlike. 
A characteristic feature of the lowland is its inland salt lakes, 
which cover large areas during the rainy season, but shrink to 
saline marshes or completely disappear during the dry season. 



M.-S. PHYS. GEOG. — 8 



XII. ISLANDS 



Classification. — As distinguished from continents the smaller 
land masses rising above the sea are termed islands. They 
vary greatly in size, from the mere protrusion of a rocky or 
low-lying mud or sand bank, a few square feet in area, to land 

masses hundreds of 
square miles in ex- 
tent, which, in their 
general character- 
istics, are not unlike 
the continents them- 
selves. 

According to their 
origin and structure 
islands may be classi- 
fied into two groups : 
(i) continental; 
(2) oceanic. 

Continental Islands, 
as their name im- 
plies, rise from the 
submerged continen- 
tal borders and not 
from the deeper parts 
of the ocean's floor. 
At earlier periods in 
the earth's history 
many of them were 
actually parts of the 
continents from which they have been separated by settling 
(subsidence), wave wear (erosion), or a combination of both. 

128 




The British Islands and the Submarine Plat- 
form ON which they rest. After Geikie. 
The tinted area is less than 100 fathoms in depth. 



OCEANIC ISLANDS 



129 



Sea exploration and soundings show that the British Islands rest upon a 
submarine platform which cannot be regarded as other than an extension of 
the mainland of Europe. This, together with their geologic structure, goes 
to show their, intimate re- 
lation to the existing con- 
tinent, of which, in fact, 
they form a part. 

Other coastal 
islands have resulted 
from the constructive 
action of the waves 
by which mud banks, 
sand spits, and reefs 
have been thrown up. 
Once above the water, 
their growth is aided 
by the springing up 
of coarse grasses and 
other forms of vege- 
tation which gradually 
collect and hold in 
place additional 
matter. 

Along the Gulf coast 
of Texas long barrier is- 
lands, broken by occa- 
sional inlets, have been 
built up by the waves 
driven shoreward by the 
prevailing winds. The 
filling up of shallow 

sounds and the present growth of islands is also well illustrated along the 
coast of North Carolina. 




Map of the Coastal Portion of North Carolina 

In this partially drowned region the outer sand reefs, in 
the form of long, narrow islands, almost completely 
close the entrances to Albemarle and Pamlico sounds. 
The inclosed bodies of water are being gradually filled 
by the silt and sand brought from the land by river 
action. 



Oceanic Islands are situated far from the continents. They 
rise from the deeper portions of the ocean's floor. In structure 
they are strikingly unlike most continental islands, being either 
volcanic or coralline. The former often rise thousands of feet 



I30 



ISLANDS 



above the sea level, while the latter are low-lying and devoid of 
surface relief. 

Oceanic islands of the first group are the tops of volcanic 
peaks which rise above the sea through their own upbuilding; 
the islands of the second group are brought to the surface by 

the upbuilding of 
coral reefs from high 
submarine volcanic or 
other platforms. 

Volcanic Islands are 
arranged, as a rule, 
along the great bands 
or belts of volcanic 
activity which trav- 
erse the globe. 

Most of them are 
found within the vol- 
canic belts of the 
Piicific and the 
Atlantic. There are, 
however, exceptions 
to this general rule, 
many volcanic islands 
being situated quite 
irregularly. The volcanoes upon islands in the Pacific belt are 
among the most active in the world ; those in the Atlantic belt 
are far less active, and many are either extinct or bordering on 
extinction. 

Volcanic islands are formed by the accumulation of materials 
thrown out by submarine volcanoes. Sometimes such islands 
are formed very suddenly, as in the case of Graham Island, in 
1 83 1, and that off the island of Santorini, in the Mediterranean, 
in 1866. 

Coral Islands are found especially in the southern Pacific and 
Indian oceans. They are a result of coral growth and wave 
action. The coral animal is ■Bl polyp ■ — not an insect, but an 





IP 


^^ 


wm 


^^B 


^^^H 












wSfk 












jW 


wk*»- 










-;3 


r'A- 










"^L 


■Wf 










-'I'^fl 












-"-.-^^^l 


^^. 










^H^H 




b. 




^ 


iMiiiiii 


jH 



liKAIN CiiKAl, 

In this figure there is shown a coral skeleton, that is, 
"dead coral," which is composed of carbonate of 
lime, the substance of limestone. The living portions 
of coral, the polyps, are soft and fragile, and when 
removed from the sea water soon dry up and disappear. 



CORAL ISLANDS 



131 



Diagrammatic 
Formation 
Atoll 



Illustrations of 
OF Barrier Reef 



THE 
AND 




animal much lower in the scale of life — which secretes from 
sea water a skeleton composed of carbonate of lime, the sub- 
stance of limestone. Many polyps are usually supported in 
common by a single skeleton, 
which may be of a delicate 
branching form or a great 
rounded mass or head. Be- 
ginning in water not exceed- 
ing 20 fathoms, more often 6 
or 7 fathoms, the reef-build- 
ing coral by the growth and 
accumulation of its hard 
parts lays the foundation of 
what may become a reef or 
a coral island. In all cases 
this coral growth rises from 
a submarine platform which 
not infrequently is the sub- 
merged summit of a volcanic 
peak. Polyps thrive best 
when immersed in pure sea 
water ; accordingly they ex- 
hibit the greatest profusion 
on the exterior or seaward 
side of a reef. As they ap- 
proach the surface, the liner 
and more delicate skeletons 
are broken by the dashing of 

the waves, and their fragments, settling down among larger 
coral heads, fill the interstices and serve eventually to cement 
and solidify the reef. Finally the level of low tide is reached 
and the upward growth of the polyps is checked. 

The further upbuilding of the reef now becomes the work of 
the waves — a work of destruction and of construction. Portions 
of coral growth are torn from their beds, broken up, ground as 
sand on a beach, and swept into a long ridge. 



Section of mountain rising above 
water, forming an island ; RR, section 
of fringing reef resting on slopes; 
A, height of sea level as shown in II 
below ; B, height of sea level as shown 
in III below. 

11 



section of mountain rising above water 
after partial submergence; RR, sections 
of barrier reef resting on slopes. 




section of same mountain after 
submergence ; RR, sections 
reef now forming an atoll. 



complete 
of same 



132 ISLANDS 

The ridge, heaped up by successive additions of broken coral, 
finally becomes so high that it overtops the waves, and an island 
is formed. 

The next stage is the appearance of vegetable life. Floating 
wood lodges among the coral fragments. It decays and forms 
mold. Seeds, such as cocoanuts, not injured by salt water, are 
wafted to the newly formed islet ; others may be carried thither 
by birds. Under the stimulus of a tropical sun they grow, and 
in time cover the dead coral mass with living green. 

The breadfruit and cocoa palm are the most important of the 
forms of plant life that flourish upon such islands. No large 
animals live upon them, and, on account of their small areas, 
they can sustain only a limited population. 

Coral Reefs may be classed as (i) fringing reefs ; (2) barrier 
reefs ; (3) atolls. 

Fringing reefs occur near the shore line surrounding islands or 
skirting the coasts of continents. Many Pacific islands furnish 
examples of such reefs as well as the eastern coasts of Africa 
and South America v/ithin the equatorial belt. 

Barrier reefs are quite like fringing reefs, but farther removed 
from the land. They represent a later stage of reef develop- 
ment when, by the action of the waves and the growth of coral, 
the reef formation has advanced seaward. In the meantime the 
inner side of the reef has been slowly dissolving away, leaving 
an ever-increasing interval of shallow water between it and the 
land. In some instances it is possible that fringing reefs may 
have been transformed into barrier reefs by the gradual subsi- 
dence of the sea bottom, whereby the reef, growing upward to 
the surface, appears at a considerable distance from the shore. 
This is illustrated by the diagrams on page 131. 

The great barrier reef off the northeast coast of Australia is 1250 miles long 
and from 10 to 90 miles wide. The island of New Caledonia and many others 
are protected from the sea by similar reefs. 

An atoll is a belt or strip of coral reef inclosing an expanse of 
water called a lagoon. 



ORIGIN OF ATOLLS 



133 



Sea -• „ . 
Level- R R Lagoon 

/ PLATFORM 




Atolls are usually nearly oval or circular, but in many cases 
they are quite irregular in shape. Sometimes, as in the case of 
Whitsunday Island, they are complete rings; but most frequently 
on the side not exposed to 
the prevailing winds there s- 

are one or more breaks, form- / "— ., ^ ,.-•'' \ 

ing inlets. 

The atolls are almost innumer- 
able. There are nearly a himdred 
of them in the Dangerous Archi- 
pelago, which lies to the westward 
of Tahiti. They are not more than 
half a mile across, from the sea to 
the lagoon. In their highest parts 

they are only a few feet above the water; still, they resist the utmost fury of 
the waves. They are thickly covered with vegetation. 

Origin of Atolls. — Many of the reefs and atolls rise from very 
great depths ; but the polyps are most vigorous in water not 
deeper than 60 feet; and in water that is more than 150 feet 



Theoretical Section of an Atoll 

I?R, reef; S, summit of island; S' , former 

summit of island. 




^ „ vsf^A y*i^«.'«>-~*^ 



Atoll 



deep they cease to live. The question, therefore,- arises, how can 
the foundations have been laid for certain reefs and atolls, which 
stand in water not less than a mile and a half deep .-' 

Darwin suggested an answer which enables us to understand 
not alone how atolls in deep water may have originated, but also 



134 ISLANDS 

how atolls in general have been formed. It is well known to 
geologists that the level of the ocean bed is subject to change. 
It may be upheaved, or, again, it may subside. Darwin conjec- 
tured that as fast as the coral reef was built up toward the sur- 
face, it was carried down by the subsidence of the ocean bed. 

Let us notice the successive steps of this process. There is 
reason to believe that in those parts of the ocean where atolls 
now abound, high mountains once towered. These mountains 
were islands. The polyps built encircling reefs around them. 
But in many cases, as they built up, a gradual subsidence took 
place, until the islands themselves disappeared beneath the waves. 
This subsidence, on the one hand, and this building up, on the 
other, may have continued for ages, and to the extent of thou- 
sands of feet, so that where the mountains then were, there may 
now be deep waters and low atolls. Thus the mountain tops 
were replaced by the lagoons, and the encirling reefs became 
coral islands. 

Tahiti affords an illustration of this process. It is a volcanic island with a 
fringing reef, the foundations of which rest upon the submarine slopes of the 
island. It exhibits the appearance which must have been presented by existing 
atolls before the subsidence of the ocean floor had carried down beneath the 
surface of the sea the mountainous islands formerly inclosed by them. 

Other views, however, have been advanced, among them those 
of Sir John Murray of the Challenger Expedition, showing that 
in the explanation of the origin of barrier reefs and atolls subsi- 
dence is not necessary. 

Through wave action any summit rising above the sea may be 
leveled so as to form a submarine platform upon which a reef 
may secure a foundation. If the eminence, usually a volcanic 
peak, is not completely leveled, there remains an island sur- 
rounded by a barrier reef. This reef is all the time broadening 
its foundation by the addition of its own waste and thus pushing 
outward into the deeper water. Should it take on an annular 
form, inclosing a lagoon, with or without an island, it forms an 
atoll. Such a coral island has resulted from simple reef building 
without subsidence. Murray entertains the view also that the 



DISTRIBUTION OF CORAL 1 35 

lagoon may be deepened by the solvent action of sea water upon 
the dead coral. 

Distribution of Coral. — The reef-building polyps are con- 
fined to tropical waters which have a temperature of not less 
than 68°. The central part of the Pacific Ocean is the scene of 
their greatest activity. They are also found in many portions 
of the Indian Ocean, in the Red Sea, and the Persian Gulf. 

Except among the West Indies, at the Bermudas, and off the 
coast of Brazil, there are none in the Atlantic. 

The area within which they are at work is not less than 25 
millions of square miles. 



PART III. —THE WATER 

XIII. PROPERTIES OF WATER 

Composition and Properties of Water. — Pure water is composed 
of two gases, oxygen and hydrogen, united in the proportion of 
one volume of the former to two volumes of the latter. It is 
represented by the chemical symbol HgO. 

Among the properties of water that especially interest the 
geographer are the following : 

(i) It changes its forms with remarkable readiness ; 

(2) it expands when passing into the solid state ; 

(3) it has great capacity for absorbing heat ; 

(4) it has great solvent power. 

Forms of Water. — Water exists in three forms or states : the 
solid, the liquid, and the gaseous. Changes of temperature of 
ordinary occurrence cause it to pass from one to another of 
these. As a solid it may fall gently as snow, muffling the young 
plants and screening them from the biting winds of winter, or 
as ice it may cover the surface of lakes and rivers, protecting 
aquatic forms of life as snow does the plants and insects of the 
land. As a vapor it passes off from the surface of the seas, 
lakes, and rivers, and even from the land itself, into the atmos- 
phere. Mantling the earth with an invisible screen, it prevents 
the too rapid escape of its warmth at one time ; or, assuming 
the form of clouds in the sky, shields it from the too great heat 
of the sun at another, and when still further condensed it falls 
as rain, supplying water to springs and rivers and necessary 
moisture to animals and plants. 

Expansion of Water. — Water expands when passing from the 
liquid state to the solid. This is probably due to the fact that 
its particles, when crystallized, do not fit so closely together as 

136 



EXPANSION OF WATER 1 37 

before. When cooled, it follows the general law, and contracts 
until it reaches the temperature of 39.2° F. Below this it disobeys 
the general law, and expands till it reaches 32°, its freezing 
point. Then suddenly it hardens into ice, and attains its maxi- 
mum expansion. 

Since ice is more expanded than water, it is lighter than water, 
and, as we all know, floats. Were ice heavier than water, it 
would sink as fast as it was formed, and our river channels and 
shallow lakes would be filled with soHd ice from the bottom to 
the top. 

Another important consequence of the expansion of water 
when freezing is that it exerts a force that is practically irresist- 
ible. It sunders the -solid rock from the foundations of the 
mountains, and crumbles it into fragments. 

Interesting examples of the effects of the force exerted by freezing water 
may be found on rocky hillsides. During thaws the crevices of rocks be- 
come filled with water. As the weather grows cold, this water freezes and 
splits the rocks. 

Iron water pipes are sometimes burst by the freezing of the water in them 
during extremely cold weather. 

Capacity of Water for Absorbing Heat. — Two effects may be 
produced by the application of heat to a body: (i) a rise of 
temperature which is generally accompanied by expansion of 
the body. Thus an iron rod placed in the fire grows warm, and 
at the same time becomes longer and thicker ; (2) a change of 
form. In this case the heat given to the body changes it from 
a solid to a liquid, or from a liquid to a vapor, without altering 
its temperature. 

We are familiar with the fact that a kettle of boiling water may be kept 
boiling for a long time before all of the water is changed into vapor, yet during 
that time its temperature has not changed, although it has absorbed a large 
amount of heat. If the vapor thus formed be condensed to a liquid, it may be 
shown experimentally that the same amount of heat will be given out as was 
originally absorbed. 

Heat which causes change of form without altering the temper- 
ature is called latent heat ; that which is absorbed by a solid 



138 PROPERTIES OF WATER 

when melting being known as the latent heat of melting, and that 
which is absorbed by a liquid when becoming a vapor, as the' 
latent heat of vapofisation. 

Take a lamp which affords enough heat to raise the temperature of one pound 
of water 1° a minute and let us call that amount of heat a unit of heat. Now 
set in a vessel over the lamp a pound of ice at 32°. It will immediately begin 
to melt, but the heat does not warm the ice or the water ; it only melts the ice. 
At the end of 143 minutes all the ice will be melted, but the temperature of the 
water will still be 32° and no more. Now, what has become of all the heat 
received from the lamp during these 143 minutes? It has gone to convert the 
solid into a liquid and is therefore called latent. The latent heat of melting 
ice is therefore 143 units. Now let the lamp continue burning as before. 
In 180 minutes the temperature will be raised from 32° to 212'"-' and the 
water will then begin to boil. 180 units of heat have therefore been re- 
quired to raise the temperature of the water from its freezing point to its boil- 
ing point. If now the boiling water be kept over the lamp it will not become 
hotter but will gradually change into vapor and at the end of 966 minutes more 
it will have boiled away. Thus the latent heat of evaporation of water is 966 
units. In other words it takes as much heat to melt one pound of ice as it 
would to heat 143 pounds of water one degree, and as much heat to change 
one pound of boiling water into vapor as it would to heat 966 pounds of water 
one degree. 

Water is peculiar in that its latent heats of melting and evap- 
oration are larger than those of any other substance and this 
is of special importance in its relation to natural phenomena. 

Evaporation and Condensation. — From the above statement it 
will be seen that evaporation e.xerts a cooling influence because 
ice or water on becoming vapor renders heat latent. 

Condensation of water, on the other hand, exerts a warming 
influence. As has been frequently noticed, the intense cold is 
mitigated just before a snowstorm. This is due to the conden- 
sation of vapor into snow. 

It has been computed that from every cubic foot of vapor 
condensed, and frozen into snow, heat enough is set free to 
raise more than 100,000 cubic feet of air from the temperature 
of melting ice to summer heat. 

Nature makes great use of these counter properties, the evapo- 
ration and condensation of water. She stores away the heat of 



CIRCULATION OF WATER 1 39 

the torrid zone among the particles of vapor, thus cooHng the 
atmosphere. Transported by winds to other regions, they are 
there condensed into rain and their heat set free to warm the 
air and modify the cHmate. 

The Solvent Power of Water is another property of great im- 
portance. The forms of plant and animal life are largely built 
up of materials which enter them in solution. Water acts as 
a vehicle for conveying these materials into the living system. 
It is essential, therefore, to the maintenance of life. 

Moreover, by the solution of mineral substances water pro- 
motes rock decay and the general disintegration of the earth's 
crust. All waters percolating through rocks or flowing upon 
the surface are more or less charged with mineral matter held 
in solution. 

Circulation of Water. — The readiness with which water 
changes its form and passes from the liquid state to that of 
vapor, and from the vaporous to the liquid state again, is the 
means whereby a constant circulation is carried on from the 
sea to the land, and from the land to the sea again. 

It waters the thirsty lands ; it fills the springs and replenishes 
the rivers. Thus some portions of the rainfall find their way 
back to their home in the sea through river channels ; other 
portions, evaporated, rise in the atmosphere and again being 
cooled descend as rain or snow. 

And thus most of the waters of the globe come out of the 
sea as from a reservoir and to it they are later returned. 



XIV. WATERS OF THE LAND 



Ground Water and Springs. — Only a portion of the rain which 
falls upon the land finds its way directly into the creeks and 
rivers leading to the sea. The larger part sinks into the earth, 




Diagrammatic Illustration of a Common or Gravity Spring 

a represents an impervious layer above which are the porous beds b, c, and d. Rain water 
percolating the soil and porous beds appears as a spring s, where tlie bed a is cut by 
the valley. 

where it is known as ground zuater, though sooner or later 
much of it again reaches the surface, chiefly in the form of 
springs. Many rocks are porous, and most rocks are traversed 
by cracks and especially by joints, consequently surface water 
percolates downward until its further progress is impeded by 
an impervious layer. Flowing, now, over the top of that 
layer in the direction of its incHnation, the water will appear 
as springs, or a line of seepage, wherever the topography is 
such as to furnish an outcrop, as on the side of a hill or valley. 
Should the rocks be alternately porous and impervious and 
incline or dip toward a fault fissure appearing at the surface 
at a lower level than their outcrop, then, under certain condi- 
tions, as when the opposite wall of the fissure is composed of 
compact or non-porous rock, the water will completely fill the 
fissure and will be forced out at the surface under more or less 
pressure. 

140 



GROUND WATER AND SPRINGS 



141 







Diagrammatic Illustration of a Fissurp: Spring 

In the figure above the porous beds p,p and the impervious 
beds c,c,c, outcropping on the right and dipping to the left, on ac- 
count of a fissure of displacement or fault, abut on an impervious 
mass m. The rain falling upon the outcrop creeps downward 
through the pervious beds/,/ until the fissure is reached, where 
the water is forced to the surface as a spring s by the pressure of 
that in the reservoirs r,r,r behind it. As will be shown later, 
the principle is identical with that of the artesian well. 




An Appalachian Mou.niaiin Si'rimj 

This beautiful spring, surrounded with ferns and other forms of vegetation, is one of many 
on the Blacli Mountains of North Carolina. From United States Geological Survey. 

The springs above described represent two types : (i) common 
QX gravity springs ; and {2) fissure springs. 



142 



WATERS OF THE LAND 



The depth to which percolating water descends is surprising. From a 
deep well sunk in a certain district of France, pieces of leaves were thrown up 
by the first gush of water from a depth of about 400 feet. These leaves were 
comparatively fresh. They were ascertained to have come from a distance of 
about 150 miles from the spring. 

From the percolation of water through the earth arises one of the greatest 
difficulties in mining operations. Before the invention of steam pumps many 
coal pits in England were abandoned because, as the miners said, they were 
drowned. From the Comstock mine 3,500,000 gallons of hot water had to be 
pumped every 24 hours. 

Artesian Wells are so called from the province of Artois in 
France, where they were first used. As in the case of fissure 

^ J c p c 




Section of an Artesian Basin 
/, /, porous beds; c, c, impervious beds above and below/,/, inclosing the reservoir, r ; 
L, water level ; W, artesian well. 

springs, their source of supply is porous, usually sandy, beds 
inclosed by impervious layers. The porous beds act as reser- 
voirs, and their outcrop may be many miles distant from the 
region in which the wells are sunk. Formerly it was thought 
that artesian conditions prevailed only in basins, as illustrated 
in the figure above, and that when the upper confining layer was 
penetrated by boring, the water should rise, fountain like, in the 
air. Theoretically it should reach the height of the water level 
in the reservoirs, but practically, on account of adhesion, friction, 
and the resistance of the air, this is not attained. 

It will be readily understood that the larger the number of 
wells sunk in a given basin, the more the pressure is reduced 
by the increased outward flow which lowers the height of the 
water in the reservoir. 

It must be kept in mind that by "reservoir" is not meant a cavity filled 
with water, but a porous rock, as a bed of sand or gravel, saturated with 
water. Through such a reservoir water flows which has fallen on its outcrop 
as rain. 



ARTESIAN WELLS 



143 




Artesian Conditions arising from the Passage of Porous Water-bearing 
Beds into Impervious Beds 

/, porous beds ; c, c, impervious beds above and below the porous water-bearing beds 
inclosing the reservoir ; c' , the region where the pervious beds gradually pass into 
impervious beds; r, reservoir; L, L, water level; W, artesian well. 

It is now well known that a complete basin does not furnish 
the only artesian condition. Beds incHning or dipping in one 
direction may grad- 
ually pass from a 
porous into a com- 
pact and more im- 
pervious state, and 
if inclosed, as in the 
preceding case, a 
reservoir may be 
formed as indicated 
in the figure above, 
from that part of the 
confined beds which 
is porous. This res- 
ervoir likewise, when 
penetrated, will fur- 
nish flowing wells 
until by over-boring 
the pressure is re- 
duced. Moreover, 
the same results may 
be attained by the 
penetration of in- 
clined porous beds 
properly inclosed, 




Artesian Well at Woonsocket, South Dakota 

The height of the column is 97 feet. From United States 

Geological Survey. 



M.-S. PHYS. GEOG, — 1 



144 



WATERS OF THE LAND 



which thin out and disappear at some point beyond the artesian 
area, as in the figure below. 

c 




Artesian Conditions arising from the thinning out of Water-bearing 

Beds 
/, porous beds thinning out at *■ ; r, reservoir; L, L, water level ; W, artesian well. 

Although originally applied to flowing wells, the term arte- 
sian is not now so restricted, but may be applied to any deep 
well, whether flowing or not, which has its source at a consider- 
able depth below the surface and depends upon the rainfall at 
a more or less distant point. 

Artesian wells have been of the greatest value in many countries, especially 
in arid and semiarid regions, where they have furnislied water not only 
for drinking purposes, but for irrigation as well. In Algiers through bor- 
ings put down by the French an abundance of water has been obtained on 
the margin of the Sahara. 

In many parts of the United States artesian wells are in common use, es- 
pecially in California and Texas. In some instances the water is obtained 
from beds dipping beneath the sea as on the Atlantic and Gulf coasts. 

Rivers receive their waters (i) directly from the rainfall as it 
runs off the surface in the form of wet-weather tributaries ; 
(2) from springs ; (3) from the melting of snow fields and glaciers. 

Most rivers are said to originate in springs, each of which 
pours forth a contribution in the form of a little streamlet. 
Influenced by gravity, streamlets seek a lower level, and uniting, 
form creeks and rivers the volumes of which are often greatly 
increased by sudden rainfalls and the melting of snow over 
a large area. In a similar manner a number of tributaries 
blending together make one great water course. Such a water 
course, with its tributary streams, is called a river system. 

Erosion means the eating or wearing away of the materials 



EROSION 



145 



which form the earth's exterior. This is brought about chiefly 
in two ways : (i)by the solvent power of the water; and (2) by its 
mechanical action when in motion. These two combined remove 
the more soluble and 
softer rocks with 
ease; and even the 
hardest cannot with- 
stand their action. 

If the soluble par- 
ticles of a rock are 
dissolved by water, 
the rock disinte- 
grates and crumbles 
away.. When, there- 
fore, a stream runs 
incessantly over 
such a constantly 
dissolving and disin- 
tegrating rock, it is 
clear that erosion 
will make rapid 
progress. Moreover, 
the rocky fragments 
torn from the stream 
bed by the mechan- 
ical action of the 
flowing water, espe- 
cially where there is a marked descent, are whirled against one 
another and the bottom and sides of the channel. And thus as 
the river flows on, the fragments become smaller and smaller. 
In the upper course of the river they may be of considerable 
size, but in the lower course they are reduced to sand and silt. 

The erosive action of rivers is most impressively illustrated by the excava- 
tion of rocky gorges. That of the Niagara and the canyons of our Western 
rivers are perhaps the most striking examples that can be offered. 

The Falls of Niagara, it is evident, were at one period about seven miles 




Characteristic Bed of a Mountain Stream 
.Cane Creek, in western North Carolina, a tributary of 
Nolicliucky River. From United States Geological 
Survey. 



146 WATERS OF THE LAND 

lower down the stream than at present. The vast volume of water that 
passes over the cliff, now falling from the height of 160 feet, both directly and 
indirectly is a powerful eroding agent. By it the gorge has been cut back- 
ward from the Ontario scarp towards lake Erie. 

Transportation. — The finer particles of eroded matter are 
carried along by the river in suspension ; that is, simply mixed 
with the water. The coarser portions are rolled onward by the 
current. This twofold action constitutes transportation. 

A river will transport eroded matter to a greater or less dis- 
tance, and in greater or less quantity, in proportion to the ve- 
locity and volume of its current. Water moving at the rate of 
eight inches per second will carry along ordinary sand. If the 
velocity be increased to 12 inches, it will roll along fine gravel, 
while a current having a speed of three feet a second can sweep 
along pieces of stone as large as eggs. In floods masses of rock 
as large as a house have been moved. 

As to the quantity of matter transported, it is estimated that of 
visible sediment the Rhone carries into the Mediterranean more 
than 36,000,000 tons annually, and of salts invisibly dissolved, 
more than 8,000,000 tons. The amount of silt carried into the 
Gulf of Mexico by the Mississippi in one year would make a col- 
umn one mile square and 241 feet high, and if the sand and 
gravel urged along the bottom be added, 268 feet. 

The removal of this matter from the surface of the valley reduces its average 
level one foot in 4638 years. 

Deposition. — The materials borne or rolled along by rivers 
are deposited at various points in the channel. The finer por- 
tions, called silt, familiar to us as muddy slime, are carried down 
as far as the mouth of the river. Farther up the stream sandy 
particles come to rest ; still higher, gravel is deposited ; and 
finally, in the upper course of the river we find stones of greater 
or less size. 

It is obvious that deposit will depend very largely upon the 
slope of the river bed and the rapidity of the current. Any- 
thing that checks the latter favors deposition. 



DEPOSITION 



147 



Changes in river courses are a frequent effect of deposition 
They occur especially in rivers that flow through alluvial lands 
Very often the course 
of such streams is 
marked by what are 
termed meanders, or 
sharp curves resem- 
bling the letter S. 
The lower Missis- 
sippi presents a strik- 
ing illustration of 
this- In some cases 
portions of the land 
are carried from one 
side of the river to 
the other, giving rise 
to important ques- 
tions of ownership. 

Sometimes, too, 
when a river is unusu- 
ally high, it may cut for 
itself a straight course 
instead of following 
its old curves. The 
portion of the former 
channel that is thus 
abandoned, closed by 
silt at each end, be- 
comes a lake, cre- 
scentic in shape, com- 
monly called a " cut 
off " or an oxbow. 

Among the important deposits of rivers are those that occur 
at or near their mouths, whether they flow into the sea or a 
lake. Here the current is checked by contact with the larger 
body of water, and, as a consequence, the silt which is readily 




Meanders, M, and Oxbow Lakes, O, of the 
Mississippi 



148 



WATERS OF THE LAND 



held in suspension by the moving water, now settles to the bot- 
tom. In this way bars are formed. 

The Mississippi, and all the rivers of the United States that 
flow directly into the Atlantic Ocean, have bars. 




A Meandkking Strkam, Crcjoked Creek, Camidk.ma 
Crooked Creek is a tributary of Owens River in eastern California. Its valley has been 
cut in volcanic rocks. In the waste-filled portion the stream has taken on the mean- 
dering condition of maturity. The manner in which such streams broaden their valleys 
is well shown by the meander e.xtending to the left from the center of the picture. 
From photograph by Willis T. I^ee, United States Geological Survey. 

So great is the amount of solid matter brought down by the Mississippi 
that a bar no less than two and a quarter miles in breadth was formed oil one 
of its outlets called the South Pass. Fleets of vessels more than 50 in 
number inight sometimes be seen, detained on the bar for weeks, waiting for 
a chance to go to sea, or to enter the Pass. The operation of towing a ship 
into the deep waters of the Gulf occupied days, and in some cases weeks. 

In 1875 Captain Eads, by the authority of Congress, constructed yV/Z/^j, or 
long walls, which narrowed and confined the current, and thus gave it greater 
velocity, and, of course, greater power to scour out the channel and carry off 
the sediment into deep water. The mouth of the Danube has been deepened 
by jetties so as to admit vessels of 20 feet draught. 



DEPOSITION 



149 



Again, when a river 
encounters a lake or 
other body of still 
water, where the silt 
deposited is not 
washed away by 
strong currents, there 
is gradually built up 
a fan-shaped deposit, 
through which, later, 
the stream may flow 
in several channels or 
distributaries. Such 
a deposit, from its 
resemblance to the 
Greek letter (A) of 
that name is called a 
delta. 

The Mississippi, 
the Nile, the Ganges, 
the Orinoco, the Dan- 
ube, the Volga, and 
many other rivers 
which flow into in- 
land seas or gulfs 
protected from the 
sweep of the tides 
and ocean currents, 
are famous for their 
deltas. 

But where there is 
a very strong littoral 
or shore current, it 
sweeps off the sedi- 
ment as fast as it 
enters the sea, and 




Thk Delta and DiSTRiBU'iARiiis ok the Nile 
The delta of the Nile has the typical A-shape. 



BRe. 



-^o^ 




" '"'north 

EAST 
PASS 



Delta of the Mississippi 

The lightly shaded portion is covered with shallow 

water. 



ISO 



WATERS OF THE LAND 



there is no delta formed. This is the case with the Amazon, 
the Plata, and with all the American rivers that empty into the 
Pacific Ocean. 

The area of deltas is often very large. That of the Missis- 
sippi is about 13,000 square miles. One third of it is still in 
process of formation, being as yet only a sea marsh. 




Section of the Mississippi 

Sediment is deposited not only upon the beds of rivers, but also upon their 
banks. This has the effect of raising the banks above the general level of the 
neighboring country. In some portions of their course both the Mississippi 
and the Po are above the adjacent fields. The land, therefore, slopes from 
the river on either side, and one goes up to it instead of down to it. 

Rapids, Cascades, and Waterfalls. — These terms are employed 




A Diagrammatic Illustration of Rapids 
The arrow indicates the direction of stream flow. The outcropping rocks are seen in 



to denote the more or less violent descent of streams in their 
passage from a higher to a lower level. 

Rapids are formed wherever the stream bed is in the form of 
a series of steps, as from the successive outcropping of hard 
strata or where a stream plunging down a declivity is more or 
less impeded by barriers of hard rock. The rapids above and 



RAPIDS, CASCADES, AND WATERFALLS 



151 




A Diagrammatic Illustration of Cascades 
The hard layers form miniature table rocks over which the water falls. The softer, thin 
bedded rocks below are easily eroded so that each cascade represents a temporary 
stage in gorge formation. 

below Niagara Falls and the rapids of the Saint Lawrence 
River afford excellent examples of this form of stream descent. 

A cascade is a low 
perpendicular or nearly 
perpendicular waterfall, 
usually one of a series 
by which a stream rather 
abruptly reaches its lower 
level. Frequently cas- 
cades result from the al- 
ternation of hard and soft 
strata in the stream bed. 
Falls of the cascade type 
are especially character- 
istic of the lake region of 
central New York. The 
glens and gorges about 
the heads of Cayuga and 
Seneca lakes afford many 
beautiful examples. 

The typical waterfall is 
perpendicular, resulting 
from the abrupt descent 
of a stream over a preci- 
pice. In regions of strat- 
ified rocks the plunge 
may be over hard rock cascade in the catskills 




152 



WATERS OF THE LAND 




iiiE American and Luna Falls, Niagara, from below 
In the foreground is the " Rock of Ages," one of the largest of the fallen limestone frag- 
ments. From stereograph copyrighted by Underwood and Underwood. Used by 
permission. 



RAPIDS, CASCADES, AND WATERFALLS 



153 




WiiiRi.rooL Rapids, Niagara River 
From stereograph copyrighted by Underwood and Underwood. Used by permission. 

layers (table rock) which are underlain by softer beds. Such is 
the case at Niagara. Here the harder upper rock is a limestone 80 
feet thick. Beneath it there is a softer rock, of about the same 



154 



WATERS OF THE LAND 





^.'fl 






^"t .:< 



Great Falls of the Yellowstone 
From photograph by Haynes. 



LAKES 



155 



thickness, made up of very thin layers, known as shale. As the 
limestone is undermined by the breaking up of the shale by frost 
and water action great fragments of the table rock drop into the 
abyss below, and thus the falls gradually retreat up stream. 
Other forms of per- 
pendicular falls, as 
in the Yosemite, are 
caused by streams 
leaping into a great 
valley excavated by 
glacial action. 

In regions of igne- 
ous rocks waterfalls- 
often result from the 
unequal resistance of 
the layers forming 
the stream bed. A 
very hard layer, such 
as basalt, overlying 
soft and non-resisting 
layers, will give rise 
to the typical per- 
pendicular fall as in 
the case of the Sho- 
shone Falls of the 
Snake River. In 
rather unusual instances dikes or walls of hard igneous rocks 
form the barrier over which streams are precipitated, as exempli- 
fied in the Lower or Great Falls of the Yellowstone. 

The Victoria Falls of the Zambezi in Africa are the most 
remarkable in the world. They are more than a mile wide and over 
400 feet in perpendicular height. The river plunges into a nar- 
row ravine running diagonally across the river bed. 

Lakes. — The formation of lake basins has been ascribed to 
many causes, some of which are as follows : ( i) great {diastropJiic) 
movements of the earth's crust, especially those producing large 




Ithaca Fall, New York 
This is a fall of the cascade type. 



156 



WATERS OF THE LAND 



downward folds; (2) theobstructionof drainage by the elevation of 
mountains ; (3) subsidence, as in certain regions affected by earth- 
quakes ; (4) the damming of valleys by glacial barriers (moraines) 




Niagara Falls in Winter 
The severity of the winter is shown by the great accumulation of ice below the falls. 



left upon the retreat of the ice; (5) depressions in glacial drift 
due to the melting of isolated patches of ice ; (6) glacial erosion ; 
(7) volcanic action. 

Lake Superior is thought to occupy a great downward fold of the earth's 
crust, or syncline. Most of the lakes in mountainous regions have resulted from 
orographic movements. The lakes of the "sunk country" near New Madrid, 
Mo., sprung into existence as a result of the well-known earthquake of 1811-12. 
In Switzerland and other mountainous regions small lakes behind glacial bar- 
riers are known. The numerous lakelets and ponds in glacial drift, as in Mas- 
sachusetts, are due to the melting of isolated patches of ice which were left 
surrounded or buried in debris upon the retreat of the glacier. Some of the 
lakes of central and western New York, as Cayuga Lake, seem to be due, in part 
at least, to the formation of rock basins by glacial erosion. Crater Lake, in the 
Cascade Range of southern Oregon, and similar lakes in other parts of the 
world, occupy extinct volcanic vents. 



FRESH-WATER AND SALT-WATER LAKES 



H7 



Fresh-water and Salt-water Lakes. — In regions where the 
precipitation or rainfall exceeds the evaporation, lake basins 



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Upper Yosemite Falls, California 
The height of these falls is variously stated as being from 1400 to 1600 feet. 

will be filled with water which, overflowing the rim or breaking 
through the barrier at some weak point, pushes onward to the 



158 



WATERS OF THE LAND 



sea, cutting, it may be, a channel through hard rocks; hence the 
presence, oftentimes, of rapids, waterfalls, and gorges. 

In the case of lake basins situated in arid regions, which are 
characterized by great warmth and dryness, the amount of water 



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Swiss Lake Scenery 

Sisikon on the Bay of Uri, Lake Lucerne. Uri-Rothstock (9620 feet) in the background. 
From stereograph copyrighted by Underwood and Underwood. Used by permission. 



evaporated is sometimes equal to that which is supplied, and 
sometimes greater. As fast as the water is poured in by the 
rivers it is carried away in the form of vapor. Such basins are 
not filled to overflowing, and consequently have no outlets. 

The water of lakes having no outlets is commonly salt. The 
water of lakes having outlets to the sea is fresh. The reason for 
this will be readily understood from the following explanation. 
Rivers carry into lakes many substances in solution of which one 
of the most common is chloride of sodium, or common salt. This 



FRESH-WATER AND SALT-WATER LAKES 



159 



is present in ordinary river water, although it cannot be tasted ; 
but if a large quantity of such water were evaporated, a small 
amount of salt would be left behind. Thus it is clear that if 
a lake have an outlet, not only is its superfluous water removed, 
but the salts dissolved in such water are also taken out. 




The Dead Sea 

On the other hand, if a lake have no outlet, then, while the 
water brought in is removed by evaporation, the salt intro- 
duced remains behind. Thus lakes having no outlet may be 
compared to the evaporating vats or troughs in which, as at many 
points on the shores of the Mediterranean, sea water is boiled, or 
evaporated by solar heat, in the manufacture of salt. The water 
passes off, the salt remains. Hence, year after year, salt lakes 
become Salter. 



Conspicuous examples of salt lakes are the Great Salt Lake and the Dead 
Sea. Both of these are heavily charged with saUne ingredients. The water 

M.-S. PHYS. GEOG. — ID 



i6o 



WATERS OF THE LAND 



of the Dead Sea is about one fifth heavier than that of the ocean, and sustains 
the human body, so that it cannot sink in it. P>om its great sahnity the Dead 
Sea is often called the Sea of Salt. But the Jordan, which supplies it, is of 
course fresh. 

The Dead Sea is situated in a depression remarkable for its intense heat, and 
the region in which the Great Salt Lake lies is very remarkable for the dryness 
of its atmosphere. In the case of both these lakes, therefore, evaporation 
proceeds at an enormous rate. 




Cayuga Lake from Cornell Heights, Ithaca, N.Y. 



Inland Seas. — Some inland bodies of salt water, however, 
have evidently been at one time parts of the ocean. These are 
properly designated inland seas. The most remarkable of them 
are the Caspian and Aral. 

When the Arctic Ocean extended, as geologists believe it did, 
southward as far as the mountains of Persia, these two seas and 
many neighboring bodies of salt water were included within its 
limits. 

Seals abound in the Caspian, and sturgeons, herrings, and 
other sea fish in both the lakes. 

Like other salt lakes, these inland seas have no outlet The 



DESICCATED OR EVAPORATED LAKES 



i6i 



Volga, the largest river in Europe, and the Ural pour volumes of 
water into the Caspian, yet its level does not rise. The Sea of 
Aral receives the Oxus (Amu-Daria) and the Jaxartes (Sir- 
Daria), yet its level seems actually to be lower than formerly. 

Many small salt lakes entirely evaporate during the summer, 
and leave their beds covered with saline incrustations. From the 




Crater Lake, Oregon 
This unique body of fresh water is situated in the Cascade Range of southwestern Oregon. 
Occupying a depression, known as a caldera, formed by the subsidence or caving in 
of a great volcanic summit — Mount Mazama — its surface is 6,239 feet above sea 
level. Its shape is somewhat elliptical, its diameters being 6J and 4J miles respectively. 
Its depth approximates 2,000 feet. A single island, in the form of a cinder cone, rises 
above its waters. There is no outlet, the steep walls of the caldera rimming the lake 
on all sides. 

dry bed of Lake Elton, in the Caspian region, 100,000 tons of 
salt are annually gathered. 

Desiccated or Evaporated Lakes. — Salt and alkaline lakes 
are usually the remnants of larger bodies of water which have 
greatly shrunken or almost disappeared on account of the arid- 
ity brought about by climatic changes. The former existence 
of such lakes is shown by easily recognized basins and shore 
Hues, as in the case of Lake Bonneville, in Utah, and Lake La- 



l62 



WATERS OF THE LAND 



hontan, in Nevada. Great Salt Lake is a survival of the former, 
while Carson, Pyramid, Winnemucca, Humboldt, and other lakes 
fill depressions in the basin of the latter. 




A Caldera, Canary Islands 

Calderas or " caldrons " are large craterlike depressions which often measure several miles 
in diameter. In some instances they seem to have resulted from violent eruptions, 
during which volcanic summits have been blown completely away; in others, they 
have evidently been formed by the subsidence or caving in of volcanic cones. See 
Crater Lake. 



The waters of Lake Bonneville, which were fresh, flowed into Snake River. 
Lake Lahontan had no outlet and its waters were probably never fresh. As 
these lakes diminished in volume, the water became more and more concen- 
trated, until the mineral matter held in solution was precipitated. The first 
substance deposited was carbonate of lime in the form of tufa. This is found 
along the ancient shores of Lake Bonneville and in inucli greater abundance 
along those of Lake Lahontan. Great Salt Lake is rich in salt (sodium 
chloride) ; the Nevada lakes are not. As an explanation of this difference, it 
as been suggested that Lake Lahontan had probably been evaporated to dry- 



OFFICES OF LAKES 



163 



ness, truly desiccated^ and that later, under slightly changed climatic conditions, 
which permitted the formation of smaller bodies of water, the salt beds that 
must have existed were buried under clay deposits, and therefore do not affect 
the waters of the present lakes. 

Offices of Lakes. — Lakes act as reservoirs and thus often- 
times prevent the flooding of rivers. The waters of the upper 




Upper Lake of Killarney, Ireland 

The Lakes of Killarney are famous for their beauty. They lie in the southwestern part of 

Ireland about 35 miles northwest from Cork. 

tributaries of a stream, swollen by recent and heavy rains or by 
the rapid melting of snow, upon reaching a lake spread out and 
are held back, in consequence of which the flow at the outlet is 
not greatly increased. As the inundations of the lower Missis- 
sippi are mainly due to the floods of its tributaries, there being 
no intervening lakes to hold back the surplus waters, it has been 
proposed to regulate its flows by the erection of impounding 
reservoirs on its headwaters. 

Furthermore, lakes act as settling basins. The water flowing 



1 64 WATERS OF THE LAND 

into a lake may be laden with sediment, even the finest glacial 
silt, but the water flowing from it will be clear, containing no 
matter held mechanically in suspension. Hence it follows that 
a lake may become completely filled with detritus brought in by 
flowing streams. When this stage has been reached, the lake 
gives place to a plain through which the supplying stream 
meanders. This is illustrated in a small way by the accumula- 
tions deposited in the reservoir behind an old dam. 

Geographical Distribution of Lakes. — In North America are 
found the vast bodies of fresh water which are called the " Great 
Lakes." 

Lake Superior, a member of this group, is the largest body of fresh water 
in the world. Its area is over 30,000 square miles. The surface of this great 
inland sea has an altitude of 602 feet, but its bottom extends below the sea 
level 406 feet. 

The northern part of the Great Central Plain of the continent 
abounds in lakes of greater or less magnitude. In the basin 
between the Rocky Mountains and the Sierra Nevada there is a 
region of saline lakes. 

In Europe, the great lake region lies in northern Russia and 
Scandinavia. Ladoga and Onega, Wener and Wetter, are the 
largest lakes of the grand division. Those of the Alps, Como, 
Maggiore, Geneva, and others are comparatively small, but famed 
for their beauty. 

Asia is noted for the size and number of its salt lakes. The 
Caspian, Aral, and Dead seas are examples. 

Of fresh-water lakes Asia has few. Lake Baikal, however, 
400 miles in length, may be compared with our own Lake 
Superior. 

Africa rivals North America in the magnitude of her great 
lakes. Victoria and Albert Nyanza, Tanganyika and Nyassa, 
are the largest. 

South America has two lakes of importance, Titicaca and 
Maracaibo. Australia is noted for its salt lakes. Eyre, Torrens, 
and Gairdner each exceed 100 miles in length. 



XV. DRAINAGE 

Advantages of Drainage. — The drainage of the land depends 
primarily upon its relief. Those countries best adapted for 
human habitation are well drained. Crops do not flourish on 
cold, damp soils, nor can human health and strength be main- 
tained where the ground is always wet. As is well known, the 
vicinity of swamps is especially unhealthful. 

For this reason a very large area of the sunny peninsula of 
Italy, called the Campagna, is almost uninhabited. From the 
days of ancient Rome until now it has remained, owing to the 
level nature of the land, and the consequent absence of any 
stream into which the waters might be directed, a vast swamp 
and a breeding ground of pestilence. 

How Drainage is Effected. — Rivers are the channels through 
which the water carried from the sea in the form of vapor and 
rained upon the land finds its way back to the sea. Every 
running stream may therefore be regarded as a kind of rain 
gauge, which measures, in a general way, the quantity of rain 
that falls upon the valley which it drains. 

The region drained by a river system is called the river basin. 
The basins of large streams are hundreds of thousands of square 
miles in area. That of the Mississippi contains nearly 1,250,000 
square miles. 

The limits of a river basin are defined by what are termed 
tvatersJieds; that is, water divides, sJied\)QAXiv from a German word 
meaning to divide. A watershed is a line of elevation, some- 
times lofty and sometimes low, which, like the ridge of a roof, 
divides the rain as it falls, and causes one portion to descend one 
slope of a country or continent, and the other portion another. 

165 



1 66 



DRAINAGE 



If on a map of North America 3'ou trace a pencil line round the sources of all 
the rivers that pour into the Mississippi from the Appalachian slope on the one 
side, and from the Rocky Mountain slope on the other, 3-ou will have marked 
out the watersheds which define the eastern and western limits of the Mis- 
sissippi basin. 

The mountains and slopes of every country determine in a 
large measure the number of its water courses, their length and 
direction, and the velocity of their currents ; in a word, their 
capacity for carrying off superfluous rain water. 

Inundations. — The inundations or floods which occasionally 

submerge large areas 
of land, and are so 
destructive to life and 
property, occur where 
the quantity of water 
to be removed exceeds 
the capacity of the 
draining rivers. Many 
rivers, as the Nile, 
the Orinoco, and the 
Mississippi, are sub- 
ject to periodical over- 
flow. So extensive 
are the inundations 
of the Po that the 
Italian engineers have 




Flooded Lands at Singac, New Jersey, on the 

Passaic River 

From United States Geological Survey. 



actually proposed a 
scheme for cutting an artificial channel to be used in case of 
emergency. 

The chief causes of floods are to be found in seasonal 
changes. They affect the rainfall and cause the melting of 
snow both on high mountains and in river basins. The sudden 
disappearance of winter snow is always accompanied by swollen 
streams. 

The melting of snow in Pennsylvania, Ohio, Indiana, and Illinois, together 
with c6pious spring rains, are annually followed by a marked rise in the Ohio 



NORTH AMERICA 1 6/ 

and its tributaries, and when the snows of the Rocky Mountains begin to 
melt, the western tributaries of the Mississippi are flooded and that stream 
experiences the "June rise." 

North America. — The bounding waters of North America 
are the Arctic Ocean, the Pacific Ocean, and the Atlantic, 
inchiding the Gulf of Mexico. These receive the drainage of 
the grand division. 

The great watershed is the Rocky Mountain system. It acts 
like the ridge of a roof, shedding the water to the east and 
to the west. All the region lying westward of it is drained 
into the Pacific and into Bering Sea by the Colorado, the 
Colun^Dia, the Frazer, the Yukon, and other rivers of less im- 
portance. 

East of the Rocky Mountains the grand division is divided 
by the Height of Land and the Appalachian Mountains into 
three slopes : a northern, inclining toward the Arctic Ocean ; 
an eastern, toward the Atlantic ; and a southern, toward the 
Gulf of Mexico. 

The region lying north of the Height of Land is drained by 
the Mackenzie and Saskatchewan and by certain streams 
which enter Hudson Bay. Southward of the Height of Land 
lies the great basin of the Mississippi, the drainage of which is 
poured into the Gulf. This basin embraces all that enormous 
area which lies between the Rocky Mountains and the Appala- 
chians. 

The amount of water carried by the Mississippi from this region into the 
Gulf of Mexico every second is 675.000 cubic feet, enough to cover about 18 
acres of ground to the depth of a foot. We can see from this how soon the 
Mississippi basin would become a desolate swamp, if it were a dead level 
untrenched by its mighty system of rivers. 

The eastern slope of the grand division, including the terraced 
plateau occupied by the Great Lakes, is drained by the Saint 
Lawrence and by a series of rivers, large and small, which flow 
from the Appalachians to the Atlantic. 

South America. — The drainage of South America, like that of 
North America, is mainly effected by three river systems. The 



1 68 DRAINAGE 

crest of the Andes is the great watershed. It Hes along the 
western edge of the grand division. Hence the drainage has 
in general an easterly flow. 

The eastern slope embraces nearly the whole of the grand 
division. It is divided into three great river basins, those of 
the Orinoco, the Plata, and the Amazon. The last contains the 
greatest river system on the globe. 

The Amazon discharges six times as much water as the Mississippi. In 
respect to volume it is the largest river in the world. It rises in the beautiful 
little lake of Lauricocha, high up among the Andes. Descending by falls 
and rapids, it reaches the region of the silvas, and then becomes a stream 
navigable for large steamers from the foot of the mountains to the sea, a 
distance of about 2200 miles. 

So great is the force of its current that its fresh waters are carried a dis- 
tance of about 200 miles from the land. An ocean current passing near its 
mouth sweeps away sediment as fast as the river brings it down. Thus 
the river's own current and the ocean current prevent the formation of a bar. 

The western slope of South America is steep and narrow. 
There is no room for long rivers, and no water for large rivers. 
The Pacific receives only a few small mountain torrents, fed by 
the melting snows of the Andes. 

Europe. — From a point in the Ural Mountains at about 
latitude 61° north, to the Valdai Hills, thence in a southwest- 
ward direction through central Europe down to the southern 
shores of Spain, an irregular line may be traced which will 
separate Europe into two great slopes. The one inclines to the 
northwest, the other to the southeast. 

All the rivers have one or the other of these two general 
directions ; and the grand division is drained into the Mediter- 
ranean, the Adriatic, the Black, and Caspian seas on the one 
side ; or into the Atlantic and Arctic oceans, and the North, 
Baltic, and White seas on the other. 

The region of the Alps is drained by four streams, the beauti- 
ful Rhine of the Germans, the Rhone, the Danube, and the Po ; 
the drainage of the low plains is accomplished by a number of 
rivers, among which the Volga, the Don, the Dnieper, and the 
Dniester are conspicuous. 



ASIA 



169 



Asia. — The grand division of Asia, like that of Europe, may be 
regarded as consisting of two great slopes, one having a general 
incline toward the north, the other toward the south and east. 

Beginning on the western shore of Asia Minor, a line may be 
drawn to Mount Ararat, thence along the crests of the Elburz 
and Hindu Kush Mountains, thence northeastwardly to the Sea 




View on the River Nile 
Water carriers filling their " skins." 

of Okhotsk, which will represent the great watershed of the 
grand division. 

Southeast of this line the Euphrates and Tigris, the Indus, 
Ganges, the Yang-tze, the Hoang, and Amur carry the drainage 
to the southward and eastward into the seas and bays of the 
Pacific and Indian oceans. 

On the northern side of the line nearly every important river 
flows in a northerly direction into the Arctic Ocean. 

Africa. — The drainage of Africa is accomplished in the 
main by the four great river systems of the Nile, the Niger, the 



I/O DRAINAGE 

Kongo, and the Zambezi. Much of the surplus water of the 
grand division, however, is removed by evaporation. 

The most interesting feature in the drainage system of Africa is the river 
Nile. But for it Egypt would be as barren as the Great Desert of Sahara. 
The river is formed by tlie junction of two streams called the White and the 
Blue Nile. The former issues from the Equatorial Lakes. The latter rises 
among the hills and the table-lands of Abyssinia. 

During June, July, and August the rains pour down in torrents upon the 
regions drained by these streams. Each is flooded. Uniting at Khartum, the 
descending torrents reach Cairo by the middle of June, and during the latter 
part of summer and in the autumn the land of Egypt is under water. 

As the flood subsides, a layer of fertilizing sediment is deposited upon the 
soil. Most of it has been washed down from the Abyssinian hills by the Blue 
Nile, which takes its name from the color which the sediment imparts to its 
waters. 

Australia is scantily supplied with rivers. The Murray and 
its tributaries are the only water courses of importance. Dur- 
ing times of drought the latter cease to flow and the main stream 
is greatly shrunken. 



XVI. THE SEA AND THE OCEANS 

Extent of the Sea. — Less than three fourths of the earth's 
surface is covered by water. This surface comprises, in round 
numbers, an area of 197,000,000 square miles, of which about 
55,000,000 are land and 142,000,000 water. All of the land, ex- 
cept 13,000,000 square miles, is on the north side of the equator. 
The northern hemisphere therefore contains approximately three 
fourths of all the known land, and two fifths only of the water 
surface, of the world. 

The extent of water that is visible to the eye at one time is not great. If 
we stand on the shore and look seaward, our view is closed in by a line in 
which sea and sky appear to meet. To this line we give the name Jiorizon; 
that is, bounding line. Its distance from us depends on our elevation. If we 
occupy a position which is elevated six feet above the sea level, our horizon 
will be three miles oiT. If we ascend a bluff or lighthouse, and so gain a point 
about 100 feet high, our horizon will be 12 miles distant. 

Saltness of the Sea. — Various solids are found dissolved in 
sea water. Of these the most abundant is common salt. Others 
are certain compounds of lime, magnesium, potassium, and 
iodine. The solid matter may be estimated on an average as 
about one thirtieth part of the whole by weight. 

Though there is little variation from the average, it seems 
to be well ascertained that there are areas, as within the region 
of the North Atlantic trade winds, for example, where the pro- 
portion of saline matter is greater than elsewhere. This may 
be expected, since evaporation ^ is there at its maximum. On 
the other hand, the proportion of salts is reduced where great 
rivers empty into the sea or where great bodies of ice melt. 

^Evaporate a small portion cf sea water until it is very much concentrated. 
Then warm a drop of this concentrated fluid on a piece of glass, and put it instantly 
under a microscope. You will see the saline substances, which have given the sea 
water its peculiar taste, crystallizing in regular shapes, as the water gradually dries 
from the glass. 

171 



1/2 



THE SEA AND THE OCEANS 



Saltness of partly Inclosed Bodies of Water. — Theoretically, 
owing to excessive evaporation, the waters of the Mediterranean 
Sea ought to contain a greater proportion of saline matter than 
the adjacent Atlantic, and such is said to be the case off the 
coast of Tripoli, where they are subject to rapid evaporation by 
the hot winds from the Libyan desert. 

In the Red Sea, too, there is a concentration of saline matter. 
No streams of any consequence flow into it, and, almost com- 
pletely landlocked, it is subject to excessive evaporation ; so that 

it exhibits a degree of 
saltiness found only 
in some salt lakes. 

In higher latitudes, 
where the evapora- 
tion is not so great, 
and where there is a 
large inflow of ter- 
restrial water, land- 
locked seas are less 
salt than the adja- 
cent ocean. Some 
parts of the Baltic, 
for instance, are al- 
most fresh. 

Color of the Sea.— 
The sea is green or 
blue ; it is sometimes colored here and there by reddish, or 
whitish, yellowish, or crimson patches, according to the tints 
imparted by the color of the bottom, by the shadow of the 
clouds, by the ingredients of its waters, or by its myriads of 
organisms. In certain parts of the Indian Ocean the waters, 
as seen from a distance, are black. 

In the Mediterranean, in the Gulf Stream, and between the 
tropics generally, the sea waters are dark blue ; along the shores 
and near the mouths of great rivers and in coral seas they are 
green. 




Phosphoresci m Si \ 



PHOSPHORESCENCE 



173 



Thus the sea assumes here and there various shades of color; 
yet its waters, when viewed by the tumblerful, are as clear as the 
purest crystal. 

Phosphorescence. — In most parts of the sea the water is 
phosphorescent. The phosphorescence is caused by certain 
minute living bodies which, like glowworms and fireflies on the 
land, have the power of emitting light, some in flashes, and 
some in a steady glow. These little creatures, invisible to the 
naked eye, are as multitudinous as the sands on the shore. 




In Arctic Ice 
Breaking out of Etah. Peary expedition. From Bulletin of the Philadelphia Geographical 

Society. 

In tropical seas and in certain waters they tip the waves with 
flame, and cover the sea after dark with sheets of light. As the 
ship plows these waters, she leaves a bright streak far behind 
in her wake. 

Though we cannot see the dolphin and other fish, as they sport in the 
depths of these phosphorescent seas, yet, by the streaks they leave behind, 



174 THE SEA AND THE OCEANS 

we can often track them through the water, as we do rockets through the air. 
As they chase each other in the mazes of their sport, these threads of light 
are, to those who are fortunate enough to see them, among the most pleasing 
wonders of the deep. They are particularly beautiful in the harbor of Callao. 

The Temperature of the Sea is in general highest near the 
surface. In the equatorial waters the average surface tempera- 
ture is about 80° F., sometimes rising in the Indian Ocean to 90°, 
and in the Red Sea to 94°. Toward the bottom the tempera- 
ture is depressed. Indeed, near the bottom all over the globe 
deep sea water seems to be about as cold as that of the polar 
seas. 

During the Arctic winter the sea is frozen to the deptli of several feet, form- 
ing floe ice, through which, by the action of the tides, currents, and winds, 
temporary channels or leads are opened. Taking advantage of these water 
ways, the explorer or navigator urges his ship onward. Oftentimes, however, 
the channels are closed with prodigious force and his vessel nipped if not 
crashed. As a result of this ice movement barriers of broken or pack ice are 
formed which may reach the height of 100 feet. 

The Oceans. — The sea is one immense body of water encir- 
cling the globe. It is, however, divided by the intervening land 
masses, or continents, into smaller bodies, called oceans. Of 
these the Pacific is the largest. It contains more than half the 
water of the sea. Next in size, but only about half as large 
as the Pacific, is the Atlantic. The Indian is the third in area. 
The Arctic is properly only an extension of the Atlantic, while 
the Antarctic hardly deserves to be regarded as distinct from the 
main body of the sea. 

The form of each ocean basin depends upon the shape of the 
inclosing continents. The Pacific approaches the oval ; the 
'Atlantic has been compared to a long trough ; the Indian is 
triangular ; while the polar oceans are very irregular. 

Of all the oceans the Atlantic is the most marked by inden- 
tations of its shores. The Asiatic edges of the Pacific and 
Indian oceans are also well supplied with bays and border 
seas. 

Depth of the Oceans. — Two questions connected with the 



DEPTH OF THE OCEANS 



175 



subject of ocean basins have been within a few years made 
matter of accurate investigation — their depth and the con- 



figuration of their bottom. 



40 LONGITUDE 30 



20 GREENWICH 10 



10.000 

zaooo 



LftBRAOOR 


JA 


1 


II 


1 







z3 


HI 










1 





Vertical Sectioiv of the Ailantic Ocean at 52'-' Nukth LATrruDE 

The average depth of the Atlantic is about 12,000 feet. It 
seldom exceeds 18,000 feet, or 3^ miles. The deepest sound- 
ing has been made 70 miles north of Porto Rico. It was 27,366 
feet, or rather more, than five miles. 

The Pacific has a somewhat greater average depth than the 
Atlantic. Like the Atlantic, it has deep abysses. Soundings 
of 27,930 feet have been made in a large depression, known as 





60 


so 


LONGITUDE 


WEST 


AO FROM GREENW 


ICH 30 


20 


10000 



10000 


sMARTINIQUE 


_= 


tetegB 




1-*-' 


F060 1 
CAPE VERD 


|(VOL.) '^ 


20.000 


^mBHWayyiaBM 


EoiiS 




WM 


rnn 







Vertical Section oi' hie Atlanitc Ocean at 14° 48' Noriti Latitude 

Tiiscarora deep, east of northern Japan and the Kurile Islands, 
and one of 30,930 in Lat. 30° 27' 7" S., Long. 176° 39' W. The 
greatest depth known, however, 3 1,614 feet, is near the island of 
Guam, a southern member of the Ladrone group. 

The Bottom of the Ocean is, hke the land, diversified with hill 
and dale. Vast plateaus, banks, and shoals spread themselves 
out; and islands rise from the ocean depths far more abruptly 
than mountains do from the lowlands. 

San Domingo and many other islands of the sea rise from 
the bottom to the surface almost perpendicularly. The Silla 
de Caracas, on the other hand, which is the steepest mountain 
in the world, rises at an angle of 53°. 

The bed of the Atlantic has been more thoroughly examined 
than any other. It seems to consist of two nearly parallel 

M.-S. PHYS. GEOG. — II 



1/6 THE SEA AND THE OCEANS 

valleys extending north and south and separated by a lofty 
dividing ridge. The islands which are scattered along its 
length are the summits of this ridge. That portion of the 
Atlantic bed to which the name of TelegrapJiic Platemi has 
long been given is of special interest. This plateau stretches 
entirely across from Newfoundland to Ireland, at an average 
depth of somewhat less than two miles. 

If we imagine ourselves walking across it from Newfoundland to Ireland, 
we shall first descend by an easy slope to the Grand Banks. Here the depth 
is about I coo feet. Leaving the Grand Banks, we shall pass quite rapidly to 
the depth of about 13,800 feet. From this point there is not much variation 
in the depth for about halfway across the ocean. When, however, we have 
performed half our journey, we shall ascend again, first rapidly and then 
gently, until we reach the neighborhood of the British Isles. For a distance 
of about 230 miles westward of Ireland the upward slope is very gradual until 
we gain the dry land. 

Note. — The practical value of the information derived from the Atlantic deep-sea 
soundings was early appreciated by Maury. Almost as soon as the results of the 
soundings were made known to him, he saw that the laying of a telegraphic cable 
was a practicable project. He was the first to suggest and urge the carrying out of 
this scheme, the accomplishment of which has been one of the grandest achieve- 
ments of modern science. To Maury belongs the glory of having pointed out a high- 
way under the waters, whereby the ends of the world have been brought into 
instantaneous communication. 

Marine Deposits may be classed as Marginal 2iX\d Abyssal. 

To the first group belong the silt and sand brought down by 
rivers, the waste of the continental borders, and the ooze result- 
ing from the wear of rocks by glacial action. To these materials 
must also be added fragments of the solid parts of marine ani- 
mals, especially the shells of mollusks. The average width of 
marginal deposits is about 150 miles, although in some regions, 
as off the mouth of the Amazon, they may reach 350 or 400 
miles. Deposits similar to those here mentioned are found in 
inland seas. 

Abyssal deposits are spread over the bottom of the deep sea. 
While largely of volcanic origin, as shown by microscopic exam- 
ination, they exist also in the form of ooze of organic origin. 
Deposits of the sea, like those of the land, are chemically modi- 



1/8 THE SEA AND THE OCEANS 

fied and take on characteristic forms. Of the abyssal deposits 
red clay is the most widely distributed. Its volcanic origin is 
shown by the presence of pumice and other igneous matter. 
Associated with the red clay are found the calcareous and silicious 
coverings of minute marine organisms. Within certain areas 
they occur in such abundance as to form a distinct ooze ; thus 
the accumulation of certain foraminifer shells, belonging to the 
Globigerhia, may give rise to globigerina ooze, a limy or cal- 
careous mass, which is represented in the earth's crust by chalk. 
Again, the great abundance of Radiolaria shells may give rise 
to a silicio7is ooze. Near the south pole there is a rather large 
area covered with a silicious ooze which has resulted from the 
accumulation of the hard parts, or coverings, of low forms of 
plants known as Diatoms. The distribution of the various marine 
deposits, including the coral sands and muds, is shown on the 
preceding page. 



XVII. WAVES, TIDES, AND CURRENTS 



Waves. — " The troubled sea that cannot rest " has ever been 
the emblem of unending movement. Waves, tides, and cur- 
rents incessantly disturb it. 

Waves are caused by the wind which strikes upon the sur- 
face of the sea, and thus produces an alternate downward and 




Breakers approaching the Shore 
Coronado Beach, San Diego, California. Point Loma on the right. 

upward movement of its waters. A mass of water moved in 
this way is called a wave. The elevated portion of the water 
is called the crest ; the distance from one crest to another is 
the breadth ; the depression between two crests is called the 
troiigJi. 

179 



i8o 



WAVES, TIDES, AND CURRENTS 



The rolling in of waves upon the beach produces the impres- 
sion that the entire body of water is moving toward the land. 
As we shall see, however, when we come to consider the sub- 
ject of tides, it may actually be receding. We must, there- 
fore, distinguish between the motion of the waves and the 
motion of the water. 

If we produce a ripple upon the surface of water in a basin, bath, 
or pond, the ripple will travel from edge to edge of the water, and 
communicate an undulating or wave movement to each portion 
of the surface. But the water itself has no progressive movement. 




Breakers on the Shore 
Coronado Beach, California. Point Loma on the right. From photograph by H. R. Fitch. 

The action of a breeze upon a field of wheat, or tall grass, 
illustrates the matter very forcibly. The wind passes over the 
field, and each stalk and blade bends alternately down and up, 
thus forming depressions and wave crests. Yet there is no 
onward movement of the stalks. 

Those portions of the water, however, which actually reach the 
shore, do possess an onward movement. Instead of being driven 
against an adjoining mass of water, they encounter the solid 
bottom. Thus the lower part of their mass is retarded, while the 
upper part moves onward, curls, and dashes as a d7raker upon 
the beach. 

The Height of Waves depends mainly upon the force of the 
wind and the depth of the water. In general they are not more 



THE VELOCITY OF WAVE MOVEMENTS 



I8l 



than 8 or lO feet high. The highest known are those off the 
Cape of Good Hope, where they are said to attain the height of 
more than 40 feet. 

The bell of a lighthouse on one of the Scilly Islands, east of Lands End, 
was wrenched off by a breaker, at the height of 100 feet. 

The Velocity of Wave Movements depends ( i ) on the velocity 
and force of the wind ; and (2) upon the depth of the water and 
its freedom from obstructions. In the open sea the advance of 




Wave Action on Partly Submerged Rocks, San Diego Couniy, California 
From photograph by H. R. Fitch. 

a wave movement is more rapid than in one obstructed with 
islands. The rate of ordinary wave travel is from 1 5 to upwards 
of 50 miles an hour. 

The wave movements of the ocean are incessant. Even where 
a perfect calm prevails, there is a ceaseless movement of the 
water, which, like a great pulse, keeps the surface constantly 
rising and falling. This heaving is commonly known as the 
ground swell of the ocean. 

Waves affect the surface chiefly. The highest waves in a 
storm have no appreciable effect in water more than a quarter 



l82 



WAVES, TIDES, AND CURRENTS 



of a mile in depth. A wave 40 feet high and a quarter of a 
mile in breadth would not, in all probability, disturb the smallest 
grain of sand lying on the sea bed at a depth of 200 fathoms. 
Force and Work of the Waves. — The heaviest billows beat 
against the shore with enormous force. They undermine and 
level cliffs, they dash great rocks to pieces and grind the frag- 
ments into gravel and sand which, distributed along the shore, 
form the beach. Sand is the common beach material, though in 




Wave Action on a Rocky Headland, La Jolla, San Diego County, Cali- 
fornia 

Note also the sandy beach in the foreground and the high surf in the center of the picture 
where the waves strike the submerged rocks. From photograph by H. R. Fitch. 

times of storm bowlders may be thrown up by the waves or 
broken down from cliffs and headlands. The shore has often 
been likened to a mill where the grinding of rocks into sand is 
a ceaseless operation. 

Under the influence of waves beaches may be extended into 
spits or points, and sand thrown up as barrier islands. The lat- 
ter are especially well illustrated by the long, narrow sand bar- 
riers of the Gulf coast of Texas. 

Under certain conditions waves also act as transporting agents. 
The presence of silicious sand on the lower coast of Florida, 
where the rocks are coralline limestone, is thus accounted for. 



THE TIDES 



183 



The Tides are great wavelike movements. They differ from 
wind waves, (i) in their extent ; (2) in their regularity ; (3) in their 
cause. In a general way it may be said that two large waves, 
each having its crest and its depression, together encircle the 
globe from north to south. These two ceaselessly chase each other 
over the broad expanse of the sea, occasioning two elevations and 
two depressions of its waters in the course of about 25 hours.^ 
From the fact that these elevations and depressions occur with 
regularity about one hour later each day, and thus rudely mark 
the time, they are called tides, from the Anglo-Saxon tid, time. 




Spring Tides 

The elevation or rising of the water is called JiigJi ox flood tide ; 
its depression or falling, loiv or ebb tide. These occur alternately 
every six hours. 

Cause of Tides. — ■ The tides are mainly due to the influence 
of the moon. The sun also has a tide-producing power, but it 
is insignificant compared to that of the moon, owing to the fact 
that the sun is 400 times farther off. 

The moon is comparatively near the earth. Let us see then 
how, in consequence of this, she affects its waters. The earth 
and moon may be regarded as two bodies revolving about a com- 
mon center of gravity c, which, owing to the greater mass of 
the earth, as compared with that of the moon, lies 1000 miles 

1 The exact time is 24 hours 52 minutes, or what is known as a lunar day, the time 
between the crossing of the meridian of a place by the moon and her appearance 
on the same meridian again. 



1 84 



WAVES, TIDES, AND CURRENTS 



within its circumference. The two bodies are exactly balanced 
at their centers, but the surface of the earth at B is 7000 miles 
from the common point about which the earth and moon revolve, 
in consequence of which there is developed a throwing off or 
centrifugal force, known to every schoolboy who has used a 
sling or whirled a bucket of water over his head, which partly 




Hu;il Tl]JE AT OSTEND, LhLi.iL M 

Ostend is noted as a pleasure resort, its beach affording excellent opportunities for bathing. 
In front of the buildings is a protecting wall. The hill-like elevations at the right are 
dunes. 

overcomes the force of gravity and permits the outward bulging 
of the water in the form of a tidal wave. At A, however, in 
addition to the sHght centrifugal tendency resulting from the 
movement about C, the tidal wave is generated by the direct 
attraction or pull of the moon. 

Halfway between the tidal wave crests or high tides, there 
are depressions, as represented in the illustration. These 
occur where the water is drawn away to form the high tides. 



CAUSE OF TIDES 



185 



They create the low tides. Like the high tides, they take 
place twice in a lunar day, at intervals of a little more than 12 
hours. 

Evidence that the moon chiefly is concerned in causing the tides 
is found in the fact that high tide at any place occurs nearly 
at the time when the moon is over the meridian of that place. 




Low Tide at Ostend, Belgium 

The receding waters have left a broad beach, now thronged with visitors. In the back- 
ground at the left, standing high above the water, is seen the landing pier. 



A marked phenomenon of the tides is that the intensity of the 
movement varies. Three days after full and new moon the flow 
or rise of the water is far greater than usual. This is explained 
by the fact that when the moon is new, as in the illustration on 
page 183, and when she is full, the sun and moon combine their 
tide-producing forces, forming what are known as the spring 
tides. During these the flow is at its maximum. When, on the 
other hand, the moon is entering her second and her fourth 




1 86 



MOVEMENT OF THE TIDAL WAVE 1 8/ 

quarters, the two forces do not act in harmony, and as a con- 
sequence the neap tides result, in which the height is much less 
than in the spring tides. 

Movement of the Tidal Wave. — Were it not for the interfer- 
ence of the continents and the variations in the depth of the 
sea, a tidal wave might be expected to follow the apparent 
course of the moon about the earth. Such a wave would then 
move from east to west with its crest extending in a north-and- 
south direction. The sea, however, is divided by the land into 
great oceanic basins of varying depths. By the continents the 
wave is deflected from its course, and according to the depth 
of the water its velocity is increased or diminished, being 
accelerated in the deeper water and retarded in the shallower. 
The movement of the tidal wave is shown on a chart by means 
of cotidal lines which connect all places having high water at 
the same time. They therefore represent the crest of the tidal 
wave. 

Speed of Tidal Wave. — Since the tides follow the moon, they 
have to travel round the earth from east to west in the same 
time that she appears to revolve round it; namely, 24 hours 
and 52 minutes. The tidal wave, therefore, in equatorial 
seas, would, if it w^ere unobstructed, and could pursue a direct 
course, travel at the rate of 1000 miles an hour. 

It must be borne in mind, liovvever, that the water in midocean has only an. 
imperceptible progressive motion ; it is the undulation, not the water, that 
travels at this high rate of speed. 

The waving grain, as it bends to the breeze, causes an undulation that 
travels across the field faster than you can run ; but the stalks are rooted ; 
they only sway backward and forward to the breeze. So it is with the deep 
sea and its swell. 

When, however, the tidal wave comes near the shores, where 
the water is shallow and confined, a change occurs. The un- 
dulation is retarded, but the motion of the water is vastly in- . 
creased, and it sweeps as a current along the continental shores 
and up the bays and rivers. The current gains in speed as the 
tidal wave loses. 



WAVES, TIDES, AND CURRENTS 



^^^ ^Ru^ 




k; 



4 -f-^ 





o5^ i 

rTv \\ilm\mtOJif' 




Atlantic Coast Tides 
Mean height, in feet. 



The current often attains unusual 
speed in passing headlands, and then 
the term race is commonly applied to 
it. Such an accelerated current moves 
from six to eleven miles an hour. 

Height of Tides. — In the middle of 
the Pacific Ocean the rise of the tide 
is sometimes less than a foot ; in the 
Atlantic, near Saint Helena, about 
three feet. On the other hand, be- 
tween the converging shores of narrow 
seas and bays the water is sometimes 
heaped up to the height of from 25 
to 40, and, in the Bay of Fundy, from 
50 to 60 feet. 

The Mediterranean and the Red seas, how- 
ever, with their narrow entrances, almost cut 
oiT the tidal wave, so that in both the ebb 
and flow are very slight. The greatest rise 
in the Mediterranean is about i .2 feet. This 
seldom occurs. 

In the Caribbean Sea and Gulf of Mexico, 
likewise, the tides are rarely three feet high, 
owing probably to the fact that these sheets 
of water are protected from the tidal wave by 
the West Indies. 

Very great differences exist be- 
tween the tides at various points of 
the same coast. On the shores of 
Florida the rise is not more than 
about three feet. It increases as we 
go northward, until we reach the 
Bay of Fundy, where it attains its 
maximum. 

At some points on the shores of 
Great Britain there are tides of great 
height and strength, while at others 



TIDES OF RIVERS; BORES 1 89 

close by, the rise and fall are barely perceptible. The rise and 
fall at Liverpool are 28 feet ; in the Bristol Channel, 40 feet ; 
at Wicklow, on the opposite Irish coast, only 2 or 3. 

To account for these differences various causes may be sug- 
gested : the form of the bottom, the projection of headlands, 
the narrowing of channels along which the tidal current is 
forced, and the position of those channels with reference to 
the direction of the tidal wave. 

A glance at the map shows, for example, that were the tidal 
wave propagated from the northeast instead of the southwest, 
the Bay of Fundy would cease to have remarkably high tides. 

The peculiarities of a shore are sometimes such as to cause a complete 
sundering or division of the tidal waters. Two currents are thus formed. 
In some cases these meet again after their division and give rise to a whirl- 
pool. Charybdis in the Straits of Messina, and the Maelstrom among the 
Lofoden Isles, are illustrations of this phenomenon. 

Tides of Rivers ; Bores. — The tides of some rivers present 
interesting peculiarities. 

They enter certain river channels with extraordinary velocity. 
People crossing the dry bed of the river Dee, in England, are 
sometimes overtaken and drowned by the inrushing water. 

The case of the Amazon is of special interest. 

The tides ascend this river to a greater distance from the sea than in any 
other river of the world. They are felt 700 miles up stream ; and the sin- 
gular phenomenon is presented of there being several tides in the river at 
the same time; for before the flood of one has reached the end of its 700 
miles' journey, __several other tidal waves, each in succession bringing high 
tide with it, have had time to enter. 

A tidal wave of great heigiit sometimes enters the mouth of 
a river and ascends its channel as a perpendicular wall of water. 
Such a tidal wave is known as a bore. Among the most remark- 
able are those of the Hoogly at Calcutta, the Garonne in France, 
the T&ien4ang in China, and the Amazon. 

At certain times bores 12 to 15 feet high come rushing into the channel of 
the Amazon on the top of the tide. Sometimes as many as five, 30 or 40 




150 Longitude 20 West 90 from CO Greenwich 30 



(igo) 



h= 




XTS OF THE SkA/^ 
W \\ . 

>F THE LAND 



^^^.^ 



■" ANTARCTIC CIRCL^' 



EXPLANATION 



Drainage into the Arctic Ocean 
" " " Atlantic " 

" " " Pacific •* 

" " " Indian " 

Land without Ocean Drainage 



Cold Currents 
Warm, " 
Counter " 



30 Longitude GO East 90 from 120 Greenwich 150 



(191) 



192 WAVES, TIDES, AND CURRENTS 

miles apart, dash up the river, capsizing small craft as they go and spreading 
consternation among the watermen. 

The bore of the Tsien-tang is even greater than that of the Amazon. It 
spans the river with a feather-white and roaring wall of water, 20 feet high, 
and travels at the rate of eight miles an hour. 

The Currents of the Sea. — There are rivers in the sea. They 
are of such magnitude that the mightiest streams of the land 
are rivulets compared to them. They are either of warm or 
cold water, while their banks and beds are water of the oppo- 
site temperature. For thousands of miles they move through 
their liquid channels unmixed with the confining waters. These 
movements are called currents. 

The mariner can sometimes detect them by the different 
color of their stream, while, if they give no such visible sign of 
their existence, he can trace them by testing their temperature 
with his thermometer. 

Classification and Course of Currents. — The chart on pages 
190, 191, exhibits a general view of the horizontal currents. 

( 1 ) There is an Equatorial Current sweeping from east to 
west on each side of the equator, and well-nigh encircling the 
globe ; 

(2) There is a slight eastward Counter Current not far from 
the equator ; 

(3) There are Polar Currents setting from the polar regions 
toward the equator ; 

(4) There are Return Currents setting from the equator 
toward the poles. 

The chart also shows that as in the case of the tidal wave, so 
in the case of oceanic currents, the shores of continents and 
islands have marked effect in modifying their normal courses. 
These are also modified by the rotation of the earth. 

If two trains are moving on parallel tracks in the same direction and with 
the same speed, an object thrown or a ball shot "point blank" from one to 
the other may strike the point aimed at. But if the train from which the ball 
is shot be going 35 miles an hour, and the other only 15, the ball from the 
first will strike in advance of the point aimed at. If the direction of the trains 



CURRENTS OF THE ATLANTIC 1 93 

be eastward, then the ball will strike a certain distance to the east of the point 
aimed at. 

This is what occurs when water starts from the equator toward the poles. 
It rotates toward the east at the speed of 1000 miles an hour. Passing to 
either pole, therefore, it has a higher speed of rotation than belongs to the 
latitudes which it reaches, and hence it has an eastward movement. 

If now we suppose the ball to be discharged from the slower train, it will 
obviously fall behind, or to the westward of the point aimed at. This is what 
occurs when water starts from either pole to the equator. It has the slower 
rotary motion of the pole, and, as it approaches the equator, it constantly 
enters latitudes which have a higher speed of rotation. They pass it by, and 
it lags to the westward. 

Hence currents moving to the poles derive from rotation an eastward trend ; 
those moving to the equator, a westward. 

In treating of oceanic currents it is important to observe the methods of 
naming them. A northeast wind comes from the northeast, a northeast cur- 
rent ^iCi?^' toward the northeast. In other words, while the winds are named 
according to the points from which they blow, currents are named according 
to the quarter toward which they flow. 

Currents of the Atlantic. — The Eqimtorial Current crossing this 
ocean between the shores of Africa and South America strikes 
the latter continent at Cape Saint Roque. Here it divides. 
One portion passes southward, following the coast line of South 
America. It is named the Brazil Current. Its waters, reach- 
ing the Antarctic regions, are carried back with the polar cur- 
rent which sets along the west coast of Africa, toward the 
equator. 

The other portion of the Equatorial Current, on leaving Cape 
Saint Roque, flows northwestwardly. It is divided by the West 
Indies. Its main section enters the Caribbean Sea' and the 
Gulf of Mexico, and from these it issues through the Strait of 
Florida as the well-known Gulf Stream. Its westerly set in the 
Caribbean Sea is so strong that near the shores vessels can 
scarcely make headway against it. 

Among the return currents which carry the ocean waters 
.from the equator to the poles, the Gulf Stream is the most re- 
markable. Issuing from the tropics, this current crosses the 
Atlantic in a northeasterly direction. On leaving the Strait of 
Florida, it takes a course nearly parallel to our Atlantic sea- 



194 WAVES, TIDES, AND CURRENTS 

board. Reaching the latitude of Newfoundland, it turns more 
directly eastward. 

Near the Azores it becomes a widely expanded drift rather 
than a well-defined, riverlike current. Here it divides. One 
branch passes southward, skirts the western shores of southern 
Europe and Africa, and then, veering to the westward, finds its 
way back into the Equatorial Current. The other passes on 
to the northeast, bathes the shores of the British Isles and 
northern Europe, and enters the Arctic basin. 

The length of the Gulf Stream, from the Gulf to the Azores, 
is about 3000 miles. Its breadth in the Strait of Florida is 
about 40 miles. In its progress it constantly increases in 
breadth, till, in the middle of the Atlantic, it is 120 miles across. 
The depth is about 2400 feet near the straits. This dimin- 
ishes as the width increases. Off Charleston it is reduced to 
1800 feet. 

In volume the Gulf Stream exceeds the Mississippi more 
than 1000 times. 

The temperature of the surface waters of the Gulf Stream, 
as they pass the Strait of Florida, is sometimes as high as 85° F. 
It is a river of warm water, and retains its warmth in a remark- 
able manner. Off Cape Hatteras, and even as far as the Grand 
Banks, its temperature is 15°, 20°, or even 30° higher than that 
of the atmosphere. 

The storing up of heat begins, no doubt, while the Gulf 
Stream is still a part of the Equatorial Current, and continues 
all the time that its waters are exposed to the tropical sun, 
whether in the Atlantic Ocean, the Caribbean Sea, or the Gulf 
of Mexico. 

From the Gulf up to the Carolina coasts the waters of the 
Gulf Stream are of an indigo-blue color ; and the line which 
marks the division between them and the edge of the inshore 
waters is sometimes so sharp that the observer can distinguish 
when one half of the vessel is in the Gulf Stream and the other 
is in the cool littoral waters. In short, the line of demarcation 
is so well defined that navigators in the olden times, when both 



CURRENTS OF THE PACIFIC 195 

instruments and methods for determining longitude at sea were 
rude, were accustomed to judge of their position by it. 

So much heat is conveyed by this stream to northern latitudes, 
that the winter climate of the whole western face of Europe is 
softened and tempered. 

The ponds of the Orkney Isles, though bordering on the parallel of 60° 
north, owing to this moderating influence, never freeze ; and the harbor of 
Hammerfest, the most northerly seaport in the world, in latitude 70° 40', is 
always open. 

On the east side of Greenland and through Davis Strait cold 
polar currents come from the Arctic Ocean to replace the warm 
water carried northward by the Gulf Stream. Off the southern 
point of Greenland these currents unite and advance as far as 
the Grand Banks. 

Here one portion of the united stream sinks below the warmer 
and Hghter waters of the Gulf Stream, and pursues its course to 
the tropics as an undercurrent. The other portion turns south- 
west and follows closely the eastern coast of North America, 
keeping between the shores and the Gulf Stream, as far south 
as Cape Hatteras, where it passes under the Gulf Stream and 
continues its way to the equatorial regions mainly as an under- 
current. 

This current supplies the markets of New England with the 
choicest fish of the sea, and gives to the coast of Maine its 
singularly cool summer temperature. 

At the Grand Banks the Arctic Current meets the Gulf Stream, and, chilling 
the vapor which' rises from its surface, produces the dense fogs which render 
this part of the ocean so dangerous to navigation. 

From the Antarctic, as from the Arctic Ocean, there is a 
constant flow of icy waters into the Atlantic basin. The South 
Atlantic Current, issuing from the Antarctic Ocean, follows the 
western shore of Africa, passes northwestwardly, and contrib- 
utes to form the Equatorial Current of the Atlantic. 

Currents of the Pacific have a general resemblance to those of 
the Atlantic. 

M.-S. PHYS. GEOG. — 12 



196 WAVES, TIDES, AND CURRENTS 

An Equatorial Cmrent starts westward from that portion of 
the ocean lying to the southwest of Mexico. Like the corre- 
sponding current of the Atlantic it divides. One branch passes 
to the southward. Bathing the eastern shore of Australia, it is 
called the East Australian Current. Between Australia and 
New Zealand it blends with the Antarctic Drift. 

The northern branch of the Equatorial Current pursues a 
course not unlike that of the northern branch of the Equatorial 
Current of the Atlantic. Passing the Archipelago off the south- 
east coast of Asia, its main body turns northeastward, and, 
sweeping past the Japanese Islands, receives from them its 
x\2saQ, Japan Current. The natives of Japan call it, from the 
dark blue color of its waters, Kuro-Shiwo, that is. Black Stream. 

The Japan Current is the Gulf Stream of the Pacific. Like 
that stream, it has the twofold office of watercarrier and heat- 
bearer. It transfers the water of the central and western Pacific 
to its northern and eastern portions ; and with its warm waters 
it softens the climate of the Aleutian Islands, and of the north- 
west coast of America, just as the Gulf Stream does that of 
western Europe. 

Passing the Aleutian Islands, the main volume of the Japan Current receives 
the name of the Aleutian or North Pacific Ctirrent, and takes a southeast- 
wardly course. Reaching the coast, it gives to southern Alaska its enormous 
annual rainfall and its abundant timber growth ; it waters Washington and 
Oregon ; and then, veering to the westward, becomes again a portion of the 
Equatorial Current. 

A Polar Current, passing either under or to the side of a 
current which enters the Arctic through Bering Strait, flows into 
the Pacific. Its course, between the Japan Current and the east- 
ern shores of Asia, is like that of the polar current which flows 
between the Gulf Stream and the shores of America, and, further- 
more, Hke the Labrador Current, it teems with fish, thereby 
vastly increasing the capacity of China and Japan to sustain 
their large populations. 

From the Antarctic a broad drift flows toward the equator. 
Off Cape Horn it divides. One branch passes into the Atlantic ; 



CURRENTS OF THE INDIAN OCEAN 197 

the other, the Hmnboldt or Peruvian Current, enters the Pacific. 
The Humboldt Current carries its cool Antarctic waters all 
along the west coast of South America from Patagonia to the 
Galapagos Islands. These waters, when they touch the equator, 
are still too cold for the growth of the coral polyp. Hence the 
whole western coast of South America is without coral reefs or 
coral formation of any kind ; though in the same latitudes, at 
a distance from the coast, where the waters are warm, coral 
thrives in the greatest abundance. 

Near and at the equator the Humboldt Current is deflected 
to the westward and becomes part of the Equatorial Current of 
the Pacific. 

Currents of the Indian Ocean. — The Indian Ocean has no 
such well-defined system of currents as the Atlantic and Pacific. 
North of the equator the direction of the flow is determined by 
the monsoons. South of the equator an Equatorial Current, 
emerging from the East Indian Archipelago, sweeps to the 
westward. Reaching Madagascar, it branches. The eastern 
fork passes to the southward and merges with the Antarctic 
Drift. The western flows along the eastern coast of Africa as 
the Mozambique Current. Leaving the Mozambique Channel, it 
becomes the Agulhas Current, and south of the Cape blends 
with the Antarctic waters. 

A branch of the Antarctic Drift, setting to the northwestward, and becom- 
ing the West Australian Current, pours its icy flow into the Indian Ocean. 

Causes of Oceanic Circulation. — The chief causes of oceanic 
circulation are to be found in the winds which, brushing the sur- 
face of the water, give rise to superficial currents. These, fol- 
lowing the direction of the prevailing winds, are further modified 
by the shape of the land masses. In this manner there are 
formed in the sea five great eddies, those of the northern hemi- 
sphere moving in a clockwise direction ; those of the southern 
hemisphere in a counter-clockwise direction. 

The trade winds blowing incessantly to the westward, and 
meeting over the equatorial regions, impart to the waters be- 



198 WAVES, TIDES, AND CURRENTS 

neath them a gentle but continuous westerly movement, hence 
the Equatorial Current, while farther to the north and to the 
south, under the influence of the prevaiHng westerly winds, the 
currents bear to the eastward. 

In those parts of the Indian Ocean that are within the mon- 
soon district the currents are controlled by the monsoon winds. 
For six months they flow in one direction, for six months in 
the other. 

Some winds produce irregular currents. Such effects have 
been observed upon rivers, ponds, or canals, in piling up the 
water on one side or at one end, and by blowing it away from 
the other. 

In great storms at sea the winds may drive the water before 
them and pile it up above its usual level. 

It has been held that oceanic circulation is largely due to 
differences in the specific gravity^ of the waters in various 
parts of the sea. That it does exert some influence seems 
probable, especially in the interchange of water between the 
equatorial and polar regions. 

Sea water when heated expands. A given volume of such 
heated water, if it contain the same proportion of salts as an 
equal volume of colder salt water, will weigh less. On the 
other hand, when sea water is chilled, it contracts and becomes 
heavier. 

The surface temperature of sea water in polar seas is about 
35° F; in equatorial, about 80°. This difference of temperature 
is permanent, and sufficient to produce a marked variation in the 
specific gravity of the water in the two regions. 

Wherever the waters in one part of the sea differ in specific 
gravity from the waters in another part, no matter from what 
cause the difference may arise, or how great may be the distance 
between two such parts of the sea, the heavier water will flow, 

1 Two bodies are said to differ in specific gravity when equal volumes of the two 
differ in weight. A gallon of salt water, for example, weighs more than a gallon of 
fresh water. A pint of water weighs about a pound; a pint of cjuicksilver weighs 
about thirteen pounds. 



SARGASSO SEAS I99 

by the shortest and easiest route, toward the Hghter ; and the 
Hghter, in its turn, will seek the place whence the heavier came. 

Sargasso Seas. — An interesting evidence of the circulation 
of the oceanic waters is to be found in what are known as Sar- 
gasso Seas, so-called from sargazo, the Spanish name for sea- 
weed. These are vast collections of drifting seaweed, which 
gather in those portions of the different oceans which are most 
free from the influence of currents. 

If bits of cork or chips, or any floating substance, be put into 
a basin, and a circular motion be given to the water, all the light 
substances will be found crowding together near the center of 
the pool where there is the least motion. Like such a basin is 
the Atlantic Ocean, with its Equatorial Current and its Gulf 
Stream. The Sargasso Sea is at the center of the whirl. 

The Sargasso Sea of the Atlantic embraces an area of several hundred 
thousand square miles ; and though the weeds are all afloat and held by noth- 
ing, yet the Sargasso remains where it was over 400 years ago, when Columbus 
passed through it on his first voyage to America. 

During Maury's researches connected with the " Physical Geography of the 
Sea," the existence of four other Sargassos was established ; namely, one in 
the Indian Ocean, two in the Pacific, and another in the Atlantic. (See 
Chart, pp. 190, 191.) 



PART IV. — THE ATMOSPHERE 

XVIII. PHYSICAL PROPERTIES OF THE ATMOS- 
PHERE 

The Composition of the Atmosphere. — Wherever we go on the 
surface of the earth we perceive that air is present. If we 
ascend above the mountain tops, or pierce the loftiest clouds, it 
is still with us. It envelops the earth. 

The entire mass of the air is commonly spoken of as the 
atmosphere. It is transparent, and, unlike water, is a mixture of 
gases and not a chemical compound. Its chief ingredients are 
oxygen and nitrogen. These elements are present in the pro- 
portion of 21 parts by weight of the former to 79 parts by 
weight of the latter, or approximately i to 4. In addition there 
are also present in the air carbon dioxide in small amount, and 
in lesser degree the rarer gases argon, krypton, and helium. 
Furthermore, ordinary air contains water vapor and dust in vary- 
ing amounts as a result of its interaction with the hydrosphere 
and the lithosphere. 

Not only does oxygen form a part of the atmosphere, but chemically 
combined with hydrogen it forms water, and in combination with several other 
elements such as silicon, carbon, calcium, and aluminum constitutes the outer 
portion of the litliosphere. Oxygen is, therefore, the most widely distributed 
of all the chemical elements. It is, moreover, the vivifying agent of the 
atmosphere, being essential to the existence of living things. 

Nitrogen, of which the atmosphere is largely composed, is to the chemist 
"inert"; that is, it does not combine strongly with other elements. In this 
particular it is the opposite of oxygen and consequently does not enter con- 
spicuously into the formation of the earth's crust. Its function in the atmos- 
phere seems to be largely that of a diluting agent, thus preventing the too 
great activity of the oxygen. 

Carbon dioxide, though normally present in the atmosphere in a small 

200 



ORIGIN OF THE ATMOSPHERE 201 

amount, is essential to plant life- It is exhaled by most forms of animal life 
and is at times generated in great abundance in volcanic regions, especially 
where vulcanicity is dying out. In large amount carbon dioxide is suffocating 
rather than poisonous, cutting off the supply of oxygen which is essential to 
life. 

Invisible water vapor is another substance found in greater or less quantity 
in the atmosphere. It results from evaporation, and is one of the forms 
assumed by water in its circulation. When chilled, this vapor collects in 
the form of minute drops, forming clouds, and upon further cooling, may be 
precipitated as rain, hail, or snow. 

Dust is one of the most common impurities of the atmosphere ; and although 
usually confined to the layers over the land surfaces, it is in some instances, 
as after certain volcanic eruptions of the explosive type, wafted for long distances 
in the upper regions of air and even far over the sea. Furthermore, it may 
be held in mechanical suspension, if sufficiently fine, for a long period — it may 
be several months. A heavy rainfall cleanses the atmosphere by washing the 
mechanically suspended particles from it, hence in arid and semiarid regions 
the air is more heavily charged with dust than elsewhere. Dust, it will be 
seen, is to the atmosphere what sediment is to water. The agitation of the 
wind pollutes the air with dust just as the stirring of the bottom of a pond 
pollutes the water with mud. 

From what has been stated it is obvious that the atmosphere over the sea 
is freest from contamination by solid matter. A microscopic examination of 
dust deposited from the atmosphere shows it to be composed of a great 
variety of substances, both mineral and organic, including certain disease- 
bearing germs. 

Origin of the Atmosphere. — If the earth originated in the 
manner set forth by the nebular theory, we can readily 
conceive that in its early stages, on account of the prevail- 
ing high temperatures, much matter now in the form of solids 
and liquids was in a vaporous or gaseous state, and that, as. a 
result of such condition, many substances were included in the 
atmosphere which are not now present. It may be conceived 
further that by chemical combination and by condensation 
from cooling — processes continued through a long period of 
time — the atmosphere would become much reduced in volume 
and, at the same time, simpler in composition. It is especially 
noteworthy that, according to this view, the primitive atmos- 
phere must have contained within its body the elements of the 



202 



PHYSICAL PROPERTIES OF THE ATMOSPHERE 



primeval sea, or the first hydrosphere, which came into exist- 
ence as a condensation from it. 

On the other hand, it is held by the advocates of the 
planetesimal hypothesis that " the substances of the atmosphere 
and ocean were originally a part of the planetesimals and 

helped to form the earth's 
mass," and that they were 
subsequently forced to the 
surface by the compression 
due to gravity and the heat 
involved in that process. 

Weight of the Air or At- 
mospheric Pressure. — 
Though a gaseous body, the 
atmosphere is influenced by 
gravity. Air, therefore, has 
weight, from which follows 
atmospheric pressure. The 
famous Galileo was the first 
to point this out, A pump 
maker wished to know from 
him why a pump would not 
raise water from a well which 
was more than 32 feet deep. 
Galileo concluded that it was 
because a column of water 
32 feet high is as much as 
the weight of the air can 
balance. 

Everywhere upon land and sea this pressure is felt. If the 
atmosphere were undisturbed and of the same density through- 
out, or if it were of a uniformly decreasing density, we might 
expect it to exert upon all points at the sea level the same 
pressure. And this it practically does, notwithstanding the 
fact that it is a medium subject to numerous and, at times, 
sudden disturbances which do not fail to manifest themselves 




ToRRiCELLi's Experiment 



THE MERCURIAL BAROMETER 



203 



in pressure variations. The average atmospheric 
pressure at the sea level is 14.74 pounds (for con- 
venience usually stated 15 pounds) to the square 
inch of surface, a pressure exceeding a ton to the 
square foot. 

The Mercurial Barometer. — This is an instru- 
ment used for measuring atmospheric pressure. 
Its construction is based upon a well-known ex- 
periment of Torricelli, a celebrated pupil of Galileo. 
He filled a tube, about three feet in length, with 
mercury. He then carefully inverted the tube, 
covering its open end with his thumb, until in- 
serted in a vessel of -mercury. When released the 
mercury fell until it was about 30 inches in height. 
This column was sustained by the weight of the air. 

In Green's Standard Barometer, here shown, the 
glass tube containing the mercurial column is, for 
protection, inclosed in a brass case. To the upper 
end of the case is attached a ring (A) for the sus- 
pension of the instrument ; to the lower end is 
appended, by means of a flange (E), the cistern. 
Through a slot (B) in the case the top of the mer- 
curial column may be seen (obscured in the figure 
by the vernier which moves in the slot) and its 
height determined by a scale graduated in inches 
and tenths of inches. For convenience and more 
accurate reading the scale is provided with a 
vernier moved by a milled head ( C). As mercury 
is affected by heat, the reading of the instrument 
must be corrected for various temperatures, hence 
a thermometer (B) is attached to the case. The 
cistern consists of an upper portion in the form of 
a glass cylinder through which the surface of the 
mercury and the lower end of the barometric tube 
may be seen. The lower portion of the reservoir, 
also protected by a brass case, consists of a wooden 



204 PHYSICAL PROPERTIES OF THE ATMOSPHERE 

receptacle terminated with a kid bag which forms the bottom of 
the mercury-containing vessel. At the lower extremity of the 
cistern case there is an adjusting screw, worked by a milled 
head {F), the upper end of which presses against a button at- 
tached to the kid bag. When the button is pressed up, the 
capacity of the cistern is diminished ; when it is withdrawn, the 
capacity is increased. To use the barometer the adjusting screw 
should be raised or lowered until the surface of the mercury 
just touches the end of the ivory peg (*), which establishes the 
zero point of the scale. 

Variations in Atmospheric Pressure. — Variations in atmos- 
pheric pressure are occasioned by changes of level and by 
changes in the weight of the air. 

(i) Effect of Change of Level. — In ascending a mountain, the 
explorer passes through a certain proportion of the atmosphere, 
and is, of course, relieved from a portion of its pressure. For 
the first 10,000 feet of ascent the barometer falls 10 inches — an 
average of one inch to every 1000 feet of ascent. For the 
second 10,000 feet the barometer would fall about 6.7 inches, the 
amount of its fall constantly decreasing as he ascends. Mr. 
Glaisher in his balloon reached a height of 37,000 feet, and then 
the barometer went down to seven inches. 

The lowest reading of the barometer ever observed upon a 
mountain was 13.3 inches, at an elevation of 22,079 feet, on 
the summit of Ibi-Gamin, in Tibet. It is easy to see that the 
amount of fall furnishes a means of measuring heights of moun- 
tains, and altitudes to which balloons ascend. 

An interesting consequence arising from the weight of the atmosphere is 
the fact that the boiling point is lowered at high elevations. At about the 
level of the sea, water boils at 212° F. At Quito, 1 1,000 feet high, the boiling 
point is 194°. On the top of Mont Blanc, nearly 16,000 feet high, it is 180°. 

This results from the diminished pressure to which water is subjected at 
great elevations. It has the inconvenient effect of making it impossible in 
such situations to cook by boiling. 

(2) Effect of Change in Weight of the AtniospJiere. — A fall of 
barometer occurs, also, when the column of air above any area be- 



PROBABLE HEIGHT OF THE ATMOSPHERE 205 

comes lighter than usual. This takes place when there is more 
than the ordinary amount of vapor in the air ; because vapor is 
lighter than dry air. Consequently, the greater the proportion 
of vapor in the air, the lighter that air will be. A lo%v barometer 
therefore usually indicates a moist, rainy atmosphere. A high 
barometer indicates that the atmosphere is heavy ; either because 
it is dry or because it is dense. 

The density, or compactness, of the air of course diminishes 
with the height. On lofty mountains it is highly rarefied, 
which means that its particles, being relieved from pressure, are 
more widely separated from one another than at lower levels. 

Persons ascending to great elevations sometimes experience a singular 
difficulty. The walls of the blood vessels burst, and there is a flow of 
blood from the nose and ears. 

This mat de montagiie^ or moimtaiji sickness, as the French call it, is seldom 
felt at a lower level than 16,000 feet, and balloon ascents have been made to a 
height of 29,000 feet before any serious inconvenience has arisen from this cause. 

Lines drawn through places which have the same barometric pressure at any 
given time are called isobars, from the Greek isos, equal, and baros, weight. 

Probable Height of the Atmosphere. — The height of the atmos- 
phere has not yet been definitely determined. Calculations 
based upon the decrease of atmospheric pressure for increase of 
altitude seem to indicate that at the height of about 50 miles the 
air would become too light to appreciably affect the barometer. 
This would apparently fix the outer atmospheric limit. On the 
other hand, there is reason for thinking that the atmosphere has 
a height much exceeding 50 miles. It is believed that meteors be- 
come visible only after entering the atmosphere. Observations 
made upon the same meteor from different points afford data 
for the calculation of its height. But since the meteor is luminous, 
this height must represent a distance within the atmosphere. 
From calculations of this character it is now thought that the 
atmosphere may even exceed 100 miles in height. While in 
its outer layers the atmosphere must exist in an extremely rare- 
fied state, there is the possibihty that some of its rarer elements 
may exceed the greater limit given above. 



206 PHYSICAL PROPERTIES OF THE ATMOSPHERE 

Atmospheric Temperature. — The process by which the air is 
warmed is compHcated and for that reason can be best understood 
by the separate consideration of each step. 

(i) A portion of the radiant heat emitted by the sun is inter- 
cepted by the earth. In its passage through the atmosphere a 
part of this heat is absorbed, thus increasing the temperature of 
that body. 

(2) The layer of air resting directly upon the terrestrial areas, 
which have become heated by the impingement of radiant heat, 
are warmed by contact with the heated surfaces (conduction). 

(3) The lowest stratum of air, thus warmed and expanded, is 
crowded from its position and borne upward by the settling of 
the cooler, and therefore heavier, air. In this manner currents 
are established (convection) which circulate to a limited height; 
that is, until the warm ascending air is cooled to the temperature 
of the air above it. 

(4) Of the radiant heat falling upon the water areas a large 
part is reflected, and passing outward through the atmosphere 
again contributes to its warming by partial absorption. This 
also may become a source of atmospheric movement. 

( 5 ) On the other hand, while the land areas are poor reflectors, 
they emit radiant heat from which, as it passes outward, the air 
exacts a contribution. 

(6) In the heating of the lower atmosphere the absorption of 
radiant energy by the dust particles plays an important part. 
As they become heated, they in turn heat the air that surrounds 
them. 

(7) Another source of atmospheric heat which must be taken 
into consideration is the absorption of heat radiated from, the 
earth by watery vapor. In this particular watery vapor is said 
to be more efficient than any other atmospheric ingredient. 
Clouds act as a protective covering, thus preventing the too 
rapid cooling of the lower atmospheric layers and the disas- 
trous results that would arise from it. 

Temperature of the Air as affected by Night. — It is during the 
day that the heat effects of solar energy are most pronounced. 



SEASONAL VARIATION IN TEMPERATURE 207 

At night the heated land surfaces are cooled by radiation, for 
like other good absorbers, they readily part with their heat, which 
radiated outward into the air serves in part to prevent its too 
rapid cooling. As the land cools, the adjacent air also cools by 
radiation to it, and the layer resting directly upon the ground is 
further cooled by contact (conduction). This is well illustrated 
during the winter season when the warming of the ground in 
the daytime is not sufficient to prevent its freezing at night. 
Then the air in contact with the frozen surface is itself 
reduced in temperature. 

Water, on the contrary, is a good reflector of solar heat, a poor 
absorber, and likewise a poor radiator. The little warming that 
takes place on the surface of the oceanic areas is not readily lost 
by radiation, in consequence of which there is not the reduction 
of temperature at night noticed on land surfaces, nor is the air 
in contact with the water so thoroughly chilled by conduction. 
Hence it follows that the range of atmospheric temperature over 
the water is not so great as over the land. 

Seasonal Variation in Temperature. — The temperature of 
the air nearest the earth also varies with the season, being 
warmer in summer and cooler in winter than in either spring or 
autumn. 

The amount of radiant heat received by any portion of the 
earth's surface depends upon the directness of the solar rays. 
When they fall vertically they give rise to the greatest heat 
effects ; as their inclination increases these effects diminish. 
At the time of the vernal equinox the direct rays fall upon the 
equator. As spring merges with the northern summer the direct 
or vertical rays fall upon portions of the earth's surface succes- 
sively nearer to the Tropic of Cancer until at midsummer (June 
21) their northern limit is reached, after which, as has been 
already explained (see p. 27), their recession southward begins. 
During this season the heat received by the earth is furthermore 
increased by the long exposure due to the lengthened days. In 
the meantime the amount of heat lost by radiation during the 
night is greatly diminished, owing to the shortness of that inter- 



208 PHYSICAL PROPERTIES OF THE ATMOSPHERE 

val. Thus the surface warms to summer temperature. Under 
these conditions, without diminishing the importance of other 
processes, special emphasis must be placed upon the heating of 
the lower atmospheric layers by their contact with the heated 
land areas. 

Although midsummer is June 21, the highest temperatures are 
usually experienced some weeks later. This is due to the fact 
that the earth, warmed in excess of its radiation, is still receiving 
radiant heat. As the season advances, however, on account of 
the increased incHnation of the solar rays and the shortening 
of the days, high temperatures cannot be maintained, hence the 
earth becomes cooler. This and the attendant phenomena serve 
also to reduce the temperature of the air. 

In the winter season the radiation from the earth is in excess 
of the warming due to the sun's energy. The earth now becomes 
chilled, and as a consequence the temperature of the air in con- 
tact with it is likewise lowered. Just as the heat of summer 
comes later than midsummer, so the cold of winter comes later 
by a few weeks than midwinter (December 22). 

Instruments used for Measuring Temperature. — The instru- 
ments used for measuring the hotness or temperature of the air, 
as well as that of other bodies, are termed thermometeTs. The 
ordinary forms are based upon the expansion and contraction of 
liquids when iniluenced by heat or cold. Practically the liquids 
employed are limited to mercury and alcohol — to the former 
on account of its high boiling point and to the latter on account 
of its low freezing point. In the less common metallic ther- 
mometers the measurement is made through the unequal expan- 
sion of thin strips of different metals, and in one instrument, at 
least, through a combination of the expansion of a liquid and 
the elasticity of a metal. 

The mercurial thermometer is that in common use. It consists of a capil- 
lary glass tube having at one end a bulb or reservoir. In the process of manu- 
facture both the bulb and the tube are filled with mercury which is heated to 
the boiling point. The tube is then sealed. When cooled the mercury will 
settle, filling the bulb and a part of the tube. 



• INSTRUMENTS USED FOR MEASURING TEMPERATURE 209 

The methods of graduating the mercurial thermometer or making the scale 
by which it is to be read, are as follows : Two points are selected as standards 
— the freezing point and the boiling point of distilled water, the latter under 
the pressure of one atmosphere, for the boiling point varies according to 
atmospheric pressure. These standards have been selected, as they can be 
easily established on any thermometer. According to the Fahrenheit scale 
(marked F. or Fahr. on the thermometer) the freezing point has been arbitrarily 
placed at 32° and the boiling at 212°, from which it follows that 180° intervene 
between the two standard points. According to the Centigi^ade scale (marked 
C. on the thermometer), which is simpler, the freezing point has been placed 
at 0° and the boiling point at 100°. The degrees of this scale, it will be seen, 
are larger than those of the preceding, the relation being 100 to 180. These 
are the scales in common use, and they may be either stamped upon the ther- 
mometer case or etched upon the glass tube. The latter plan is preferable 
and is pursued in graduating the bfest instruments. 

Cheap thermometers are useful in a general way, but accurate 
readings should not be expected from them. Furthermore, if 
trustworthy results are to be obtained, the thermometer must be 
properly located. It should never be placed where the air will 
be influenced by any warming body, and especially should it be 
protected from the direct rays of the sun. If possible, it ought 
to be hung in a shelter, raised above the ground, and placed 
apart from buildings, so constructed as to permit the ready cir- 
culation of the air. When this cannot be done, the shelter may 
be built out from the north window of a building, if in other 
respects the location is desirable. 



XIX. CLIMATE 

Weather and Climate. — The atmospheric conditions prevail- 
ing at a place during a given time — a day, a month, or even a 
year — constitute its iveatJier. Within this term are included 
various elements ordinarily perceptible to the senses, such as 
temperature, moisture or dryness, clearness or cloudiness, the 
presence or absence of wind. Climate is more comprehensive, 
as it includes " an aggregate of weather conditions " based upon 
observations extending over a series of years. The longer the 
periods of observation, the more valuable become the data upon 
which climate is established. 

The chief elements of climate are temperature and moisture, 
of which the more important is temperature. 

The principal causes which modify temperature are, distance 
from the equator ; distance from the sea ; prevailing winds and 
ocean currents ; and height above the sea level. 

Distance from the Equator. — The first and most apparent 
cause of the differences in climate is the distance from the 
equator. This has two effects: As the distance increases, (i) 
the average annual temperature falls; and (2) there are greater 
contrasts between summer heat and winter cold. 

As the area within the tropics receives the vertical rays of 
the sun, it is the region of the greatest heat. Between the 
tropics and the polar circles the sun's rays fall obliquely and 
therefore exert a feebler power. Within the polar circles the 
inclination of the sun's rays is greatest, hence, except during a 
brief period of a few weeks, excessive cold prevails. 

The contrasts between summer heat and winter cold are 
mainly due to variations in the length of the day, and these 
depend on distance from the equator. Within the tropics there 



DISTANCE FROM THE SEA 211 

is comparatively little difference between the two periods of 
day and night through the year. Only twice in the year, at the 
equinoxes, are they equal for other parts of the globe. 

As the sun passes northward from the equator, the day 
lengthens over the northern hemisphere, until, within the Arctic 
circle, the sun does not set at midsummer. The same phenome- 
non occurs in the southern hemisphere, after the sun passes 
southward of the equator. 

Since there is very little difference between day and night at 
the equator, the temperature within the tropics is nearly uni- 
form throughout the year. 

North and south of the tropics there are important differences 
between day and night, in consequence of which climatic con- 
trasts are found in all regions outside of the tropics. 

Within the polar circles these contrasts are at their maxi- 
mum. The Arctic summer, strange to say, is exceedingly 
warm. It is marked by a rapidity of plant growth that is 
marvelous. In a few weeks crops mature which require twice 
that length of time in latitudes much nearer the equator. But, 
on the other hand, the winter cold is correspondingly excessive. 

Distance from the Sea. — In certain countries climate is 
affected more by distance from the sea than by distance from 
the equator. 

The climate of a region adjacent to the sea is called an msular 
or maritime climate. The climate of a region remote from the 
sea is called an inland or coutijiental climate. 

Certain causes moderate insular climates. 

(i) Water absorbs heat much more slowly than the land, 
and therefore remains, in hot weather, comparatively cooler. 
Hence the summer temperature of a country bordering on the 
sea is lowered. 

(2) On the other hand, water parts with its heat by radiation 
much more slowly than the land, and therefore remains in cold 
weather comparatively warmer. Hence the winter of a mari- 
time country is moderated. 

(3) Vapor is incessantly rising from the sea, and, being con- 

M.-S. PHYS. GEOG. — I T, 



212 CLIMATE 

densed, falls as rain or snow upon the land, and this liberates 
latent heat. 

(4) The vapor in the atmosphere of a maritime climate pre- 
vents the escape of heat. It acts as a blanket. A familiar 
illustration of this is the fact that frost rarely occurs on cloudy- 
nights. 

(5) Again, the process of evaporation goes on more rapidly 
in hot weather than in cold, and this has the effect of moderat- 
ing the summer heat of a maritime country. 

For the above reasons, insular or maritime climates are 
equable, or free from extremes. 

Inland or continental climates are the opposite of maritime. 
They are subject to great extremes, intense heat in summer and 
excessive cold in winter. 

Two reasons maybe assigned for this : — 

(i) Countries far from the sea are without its cooling influence 
upon their summer heat, and they have no reservoir of warmth 
to compensate for their rapid radiation of heat in winter. 

The continent of Asia affords the most striking instances of the excessive 
character of inland climates. The Russian army advancing toward Khiva in 
1839-40 experienced vicissitudes of temperature from a heat of over 100° F. 
to a cold of 45° below zero. 

At Werchojansk, eastern Siberia, the culminating point of excessive climate 
in all the world is reached. The extreme temperature of 90.4° below zero has 
been observed there. The soil is permanently frozen to the depth of 380 feet. 
In the month of June the Lena is free from ice ; the surface soil has thawed 
for three or four feet ; and the warmth of the short summer is such that grain 
will ripen in the shallow stratum of soil above the frozen mass. The mean 
temperature of July at Yakutsk is 69°, the same as at Paris. 

(2) The comparative dryness of the air of an inland region 
contributes to create extremes. This is strikingly illustrated by 
the climate of the Sahara. The air there is perfectly dry. No 
vapor hinders the reception of heat by day or its loss by night. 
Travelers who have suffered from intense heat during the day 
have found the water in their canteens frozen before morning. 

Prevailing Winds and. Ocean Currents. — The climate of a 
country is also greatly modified by the prevailing winds and the 



HEIGHT ABOVE THE SEA LEVEL 213 

neighboring ocean currents. If the prevaiHng winds come from 
the sea, they temper the extremes of heat and cold. If a cold 
current bathes any portion of the shore, it lowers the tempera- 
ture ; a warm current raises it. 

The British Isles and the province of Labrador are the same 
distance from the equator, and in many parts the same height 
above the sea. Yet such is the difference of climate between 
them, that Labrador is covered with snow for nine or ten 
months every year, and is so cold as to be almost uninhabitable ; 
while in England the ground is rarely covered with snow, and 
the pastures are green all the winter. 

Both countries are in the regions of westerly winds ; but in 
Labrador they come from the land, and are dry and cold ; in 
England they come from the sea, and are laden with moisture 
and warmth. The shores of Labrador are washed by a cold 
Arctic current ; those of Great Britain by the warm waters of 
the Gulf Stream and Atlantic Drift. 

The climates of western Europe, from North Cape to the 
Strait of Gibraltar, are modified by the sea winds and the in- 
fluence of the Drift. 

Norway stretches beyond the 70th degree of north latitude ; yet the west- 
erly winds are so richly laden with warmth and moisture from the waters of 
the Drift that the harbor of Hammerfest, latitude 70° 40', is never frozen, even 
in the severest winters. But cross the Scandinavian mountains, and there is 
encountered at once, if it be winter, the severest cold. In this short distance 
from the warm waters and the west winds of the Atlantic, the Russian lakes 
and rivers, the gulfs and bays of the Baltic, are found closed to navigation 
every year from November till May. 

Climatic conditions similar to those which affect the western 
shores of Europe are found upon the western slopes of Oregon, 
British Columbia, and Alaska. Westerly winds prevail, and 
they are laden with moisture from the Pacific Ocean. The result 
is that here, as in Norway, open harbors and evergreen hills 
are found in the high latitudes of Alaska and other parts of our 
northwest coast. 

Height above the Sea Level. — Among other circumstances, 
climate depends upon height above the sea. A change of ele- 




160 180 



160 110 120 100 80 6» ^° ' 



(214) 




(215) 



2l6 CLIMATE 

vation of a few thousand feet at the equator produces a change 
of temperature as great as would be experienced in sailing 
6000 miles to the frozen regions of the poles. 

The island of Cuba and the Mexican mountain of Orizaba 
are in the same latitude. The summit of the mountain is cov- 
ered with snow all the year ; the island with fruits, flowers, and 
evergreens. 

The reason why elevation above the sea level causes reduc- 
tion of temperature is that the radiation of heat goes on from 
elevated parts of the earth's surface more freely than from its 
lower portions. Two causes may be assigned for this: (i) ele- 
vations are comparatively small, and therefore have a smaller 
store of heat; (2) the air and vapor upon elevations are rare- 
fied, and hence little hindrance to radiation is presented. 

The general rule as to the effect of elevation is this : for 
every one hundred yards of perpendicular ascent there is a 
decrease of one degree in the temperature; so that, even at 
the equator, by ascending to the height of about 16,000 feet 
above the sea, one may reach the snow line. 

Isothermal Lines. — From thermometric observations made 
in all parts of the world, the actual distribution of temperature 
over the globe has been ascertained. To show this, Humboldt 
constructed a series of lines called isothcnns, or Ihics of eqjial 
heat. These are drawn round the globe so as to connect all 
places which have the same mean temperature during the year 
or any given part of the year. 

Isothermal lines are far from coinciding with the parallels 
of latitude. Let us take by way of illustration the line in the 
northern hemisphere indicating the mean annual temperature 
of 50°. (See chart, pp. 214, 215.) It passes through Oregon 
on the Pacific shores, and leaves the Atlantic coast between New 
York and New Haven. It bends northward in crossing the 
Atlantic, and in Europe passes through Liverpool, Vienna, and 
Odessa, and in Asia, near Pekin. 

The summer isotherms cross Great Britain as east-and-west lines. The 
winter isotherms are nearly north-and-south lines. 



ZONES OF TEMPERATURE 217 

We are not to conclude, however, that because the same 
isothermal line passes through two places, they have a climate 
identically the same. Of two such places one may have an 
extremely hot summer and a correspondingly cold winter. The 
other may have a climate free from extremes. Yet both may 
have the same average yearly temperature. 

San Francisco and Washington have the same mean annual temperature, 
while their climates differ greatly. 

Again, the same isothermal line passes through New York and Dublin. 
Yet the climates of these places have no resemblance. The mean winter 
temperature of Dublin is 6° above that of New York ; while the summers 
of the two places are so unlike, that whereas grapes and Indian corn are 
successfully cultivated in the vicinity of New York, they will not ripen in 
the open air at Dublin. 

Zones of Temperature. — By means of isotherms we define 
the zones of- temperature. They are indicated by the colors 
on the chart. The true Torrid Zone is bounded by the iso- 
therms of 70° on either side of the equator. The true Tem- 
perate Zones extend from the isotherms of 70° to those of 32° ; 
the Frigid Zones from these to the poles. 



XX. ATMOSPHERIC CIRCULATION 



Winds. ^ — A body of air in motion is called a wind.. The 
rate of motion and the direction of winds vary greatly. By 
means of an instrument called the anemometer, it has been as- 
certained that the velocity of a light wind is 5 miles an hour ; 

of a stiff breeze, 25 miles; of 
a storm, 50 miles ; and of a 
hurricane, 80 to 100 miles, or 
even 100 to 150 miles. 

Again, the direction in 
which winds blow is so con- 
stantly changing that they 
are often spoken of as fickle, 
inconstant, and uncertain. 
There is, however, order in 
the movements of the atmos- 
phere. The fickle winds are 
obedient to laws. There are 
causes that make them blow 
with greater or less rapidity ; 
there are reasons why they 
blow now north or south, now 
east or west. 

Winds are named according to 
the quarter from which they blow. 
A west wind comes from the west; 
an east wind from the east. 




Anemometer 
This instrument, which is used for determin- 
ing the velocity of the wind, is placed in 
an unobstructed, elevated position, as 
above the roof of a high building. It 
consists of four hollow hemispherical 
cups mounted vertically on arms which 
are attached to a vertical axis. The 
lower portion of this axis communicates 
the motion of the rotating cups, by means 
of an endless screw, to a series of dials 
which register the number of revolutions. 



Cause of Winds. — The chief 
cause of winds is the unequal distribution of heat in the atmos- 
phere. The underlying principle is illustrated by the following 
examples. 

218 



GENERAL CIRCULATION OF THE ATMOSPHERE ^^i 

If a fire is lighted on the hearth, the air within the chimney 
will be heated and forced upward by an indraught of cooler 
and heavier air from all parts of the room. This continues as 
long as the fire burns. 

The same occurs when a bonfire is lit, or a house is on fire. 
Every child knows that " the sparks fly upward to the sky." 
They are carried up by the hot ascending currents. The air 
above the fire is expanded, rendered lighter, and driven upward 
by currents of cool air that come rushing in from all sides. 
These, when heated, ascend with such force as to carry up 
clouds of smoke and sparks. 

This unequal distribution of heat, as in the warming of the air within the 
chimney while that in the room is comparatively cold, establishes a system of air 
currents. If there are no obstacles in the way and if these currents are neither 
chilled nor heated in their course, they will go straight toward the mouth of 
the chimney. Chairs and tables as well as other objects in the room will 
deflect them and cause more or less irregularity- in their direction. 

To prove that such currents really do flow, place a lighted candle in the 
doorway of a room in which a fire is burning. The flame will be drawn 
inward by the current. 

Now what occurs in the air of a room when a fire is kindled 
on the hearth takes place in the atmosphere. Some portions 
of it are always more heated than others; and the unequal distri- 
bution of heat establishes a system of currents. The heated 
surface of the earth warms the air above it. This air, forced 
up by the surrounding cool air, ascends as a current ; and streams 
of cooler, heavier air flow in. In proportion to the size of the 
area heated, the volume of the inflowing currents will be greater 
or less, and in proportion to the difference of temperature 
between the heated air and the inflowing currents, the rapidity 
of their flow will be greater or less. 

General Circulation of the Atmosphere. — Turning now our 
attention from these simple illustrations to the general circulation 
of the atmosphere, we find that within the tropics there is per- 
petual summer. Here the air is heated and filled with watery 
vapor, while the air on either side is cool and comparatively dry. 



ATMOSPHERIC CIRCULATION 

What must be the effect of this unequal distribution of heat and 
vapor ? There can be but one answer : it creates a general 
circulation of the atmosphere. In the first place, as in the case 
of the fire upon the hearth, the heated, moist air of the tropics 
is pressed upon by the heavier air on either side. It is forced 
upward, and there is an indraught both from the north and the 
south to supply its place. 




Circulation of the Atmosphere 



If the earth were at rest, and if its surface were covered with 
water, the inflowing currents would go straight from the polar 
to the equatorial regions. There would then be a simple circu- 
lation of light air from the equator to the poles, and of heavy 
air from the poles to the equator. The winds would be steady 
and unvarying. 

But the earth is not at rest, and its surface, instead of being 
uniformly covered with water, is varied by land masses of greater 
or less magnitude and elevation. The rotation of the earth and 



CONSTANT OR TRADE WINDS 221 

the influence of its land masses are two causes which largely 
affect the circulation of the air and render it exceedingly com- 
plicated. 

Winds are classified, according to the regularity with which 
they blow, as constant, variable, and periodical. 

Constant or Trade Winds. — Certain of the winds blow with- 
out interruption in the same direction and at nearly the same 
rate. So constant are they that vessels often sail in them for 
days without, as the sailors say, " changing a stitch of canvas." 
It was the steady blowing of these winds which so alarmed the 
crew of Columbus on his first voyage to America, and led them 
to fear that they would never get back to Europe. From their 
always pursuing ane trade, i.e. path, or from their importance 
to navigators, these winds have been called trade winds, or the 
trades. 

If the earth had no daily motion, these winds would blow on 
one side of the equator from the north ; on the other side from 
the south ; and in both instances, directly into the equatorial 
regions. But, in consequence of diurnal rotation, the air, when 
it arrives at the equator, is in a region which is moving toward 
the east 120 miles an hour faster than in latitude 30°, where it 
began to blow as trade winds. In thus passing from regions of 
lesser velocity to a region of greater velocity the trade winds 
are deflected toward the west, becoming in the northern hemi- 
sphere northeast winds and in the southern, southeast winds. 

Variable Winds. — North and south of the trades are the 
zones of the so-called variable winds. They extend from the 
parallels of 30° north and south, to the polar circles. Within 
these limits the prevailing direction of the winds is counter or 
opposite to that of the trades ; that is, from the southwest in 
the northern, and from the northwest in the southern hemisphere. 
For this reason these winds are called counter trades. They 
are also known as anti-trades and prevailing ivesterlies. 

Their origin is thus explained : While the trades blow stead- 
ily from the poles, there must be return currents from the 
equator to the poles, otherwise the polar regions in time would 



222 ATMOSPHERIC CIRCULATION 

be destitute of air. When the upward current at the equator 
has risen to a considerable elevation it divides and flows toward 
the poles, one part going toward the north, and the other 
toward the south pole. 

These two streams of air remain upper currents as far as 
the northern and the southern limits of the trade winds ; 
that is, about as far as the parallels of 30° north and south. 

Here, for the reason that their temperature has fallen below 
that of the air inflowing from the poles, they descend and blow 
as surface winds. They become variable, since they are fre- 
quently interrupted by great swirls or cyclonic movements 
following in the same general course ; that is, from the south- 
west to the northeast. 

That the upper currents above alluded to do flow out northward and 
southward from the equatorial regions is abundantly proved. Sometimes 
volcanoes, as we have already learned, eject vast quantities of dust. Not 
unfrequently this passes into very elevated regions of the atmosphere ; and 
instances are on record of its being carried sometimes for hundreds of miles 
in a direction opposite to that of the surface winds. 

Conseguina, in Guatemala, is in the region of the northeast trades. Dur- 
ing the eruption of 1835, its ashes were carried to the island of Jamaica. 
Jamaica is 800 miles northeastward of Conseguina. No other explanation 
of this is possible, except that an upper current was blowing above the sur- 
face winds, in a direction opposite to theirs. 

Again, in 181 5, ashes from a volcano in the island of Sumbawa, near Java, 
were borne to the island of Amboina, 800 miles to the northeast, although 
the southeast wind was then at its height. This again proves that there must 
have been a powerful current toward the northeast, above the southeast 
surface wind. It is clear, therefore, that return currents flow from the 
equator to the poles. 

Were it not for the earth's rotation, the counter trades would 
move straight to the poles. They are, however, influenced by 
that force and so deflected as to blow from the southwest or 
west. This is explained as follows: In the equatorial regions 
these winds have acquired the rapid rotary motion toward the 
east which belongs to that portion of the earth. Hence, when 
they reach the latitudes nearer the poles, they are blowing east- 



THE CALM BELTS 223 

ward with a velocity far more rapid than that belonging to 
those regions, and thus become westerly winds. 

The polar winds are currents of cold air making their way 
from the poles toward the equator. Their direction is similar 
to that of the trade winds, northeast in the northern hemi- 
sphere, and southeast in the southern hemisphere. Coming 
from the equator, the counter trades bring moisture and 
warmth ; the polar winds are dry and cold. 

The trades, counter trades, and polar winds, though treated 
separately, are really only parts of a great atmospheric move- 
ment which is ceaselessly accomplishing its unending circuit 
from the equator to the poles, and from the poles back to the 
equator. 

The Calm Belts. — Between the northeast and the southeast 
trade winds there is a belt of calms encircling the earth known 
as the Equatorial Calm Belt. The name is not altogether good, 
for throughout the entire region a vast current of air is ascend- 
ing. It is therefore an area of low barometric pressure, and 
is calm only in the sense of being comparatively free from 
the horizontal movements of the atmosphere or those that are 
ordinarily recognized. 

The portion of this belt resting upon the sea is the most 
difficult part of the ocean for sailing vessels to cross. By 
sailors it is called the doldrums. Ships are sometimes detained 
here many days. 

Between the trades and counter trades, in each hemisphere, 
there are also belts of atmosphere marked by the prevalence of 
calms. The belt in the northern hemisphere is known as the 
Calms of Cancer ; that of the southern, as the Calms of Capricorn. 
These calms, where they occur on the ocean, are termed by sea- 
faring men horse latitudes. Here, unlike the Equatorial Calm 
Belt, the air currents are descending and the area is one of 
high barometer. 

The position of all the calm and wind belts above described 
is not invariably fixed. They all move northward and south- 
ward, following the apparent course of the sun. They reach 



224 ATMOSPHERIC CIRCULATION 

their farthest northward limit in autumn, then" farthest southern 
limit in spring. 

The Periodical Winds are those which blow for a certain time 
in one direction, and then for an equal or nearly equal time, in 
the opposite direction. They are the land and sea bi^eezes and 
the monsoons. 

Along the coast of most countries there is a breeze from the 
sea by day and from the land by night. The rays of the sun 
heat the land more readily than they do the water. The warm 
rocks, sand, and soil heat and expand the air in contact with 
them, rendering it light. Pressed upward by the cooler air of 
the sea, it rises. Currents then rush from off the sea to supply 
the place of the ascending columns, precisely as the indraught 
to a furnace supplies the rush up the chimney. Thus a sea 
breeze is produced. 

At night this action is reversed. The land has the property 
of radiating, that is, of parting with, its heat more rapidly than 
the water, hence the land by night grows cooler than the sea. 
It then cools the air above it. But the air over the sea remains 
comparatively warm and light and is therefore pressed upward 
by the cool air from the land in the form of seaward-blowing 
currents. They constitute the land breeze. ■ 

Were it not for these refreshing breezes, many countries along 
the seacoast would be uninhabitable. 

Monsoons are winds which blow from a certain direction 
for part of the year, and for the rest of the year from quite an- 
other quarter. They are land and sea breezes on a grand scale. 
Instead of alternating with day and night, they alternate with 
summer and winter, hence their name, from an Arabic word 
meaning season. 

The most famous monsoons are those of southern Asia. In 
India they blow from the northeast for six months of the year, 
and from the southwest for six months. 

During the summer the sun plays upon the great deserts and 
inland basins of central Asia. Those dry and barren wastes 
glow like furnaces, and the heated air ascends from them in 



THE PERIODICAL WINDS 225 

immense columns. A disturbance is created which is felt to 
the distance of 2000 or 3000 miles from its center. Cooler air 
rushes in from the sea on three sides of the continent. Along 
the coasts of Siberia it comes from the north. From China 
round the south of the continent to the Red Sea, it comes from 
the Pacific and Indian oceans ; that is, from the southeast, 
south, or southwest. 

In this region, which is largely in the zone of " trades," the 
effect is so grea,t as actually to reverse the trade wind and cause 
it to blow in the contrary direction. 

In the winter the center of Asia is a region of low tempera- 
ture. Its atmosphere is dry, cold, and heavy ; that of the 
seas south and east -of the continent is moist, warm, and light. 
The light air is pressed upward hy the heavy, and ascends 
into the upper regions of the atmosphere. Currents then blow 
from the land toward the sea. In consequence of this we 
have, during the winter in India, the northeast monsoons, 
which are really the northeast trades blowing with augmented 
force and velocity ; on the Chinese coast we have the northwest 
monsoons. 

The summer or the southeast and southwest monsoons, hav- 
ing passed over the sea, are laden with moisture, and are the 
wet monsoons. They give its %vet season to southern Asia. 
The northeast and northwest monsoons are for the most part dry, 
because they come from the land. During their prevalence it is 
the dry season. The changing from the dry winds to the wet 
is called in India the "bursting " of the monsoon. 

The southwest monsoon sets in generally toward the end of April, a steady 
wind sweeping up from the Indian Ocean and carrying with it dense volumes 
of vapor. The atmosphere becomes close and op^Dressive. Flashes of light- 
ning play from cloud to cloud. The wind suddenly springs up into a tempest. 
Then a few great heavy drops of rain fall ; the forked lightning is changed to 
sheets of light, and suddenly the flood gates of heaven are opened, and not 
rain, but sheets of water, are poured forth, refreshing the parched earth, carry- 
ing fertility over the surface of the country, filling the wells and reservoirs, and 
replenishing the dwindling rivers and streams. The whole land from Cape 
Comorin to Bombay seems suddenly recalled to life. 



226 ATMOSPHERIC CIRCULATION 

Certain other winds resembling the monsoons are those of 
Australia, the Gulf of Guinea, and the Mediterranean. They 
are sometimes called minor monsoons. 

The winds of Australia blow landward in the hot months ; seaward in the 
cold season. They are largely controlled by the great desert of Australia at 
the one season and by that of Gobi at the other. During the South Temper- 
ate summer the Australian desert is the hotter. During the South Temperate 
winter Gobi is the hotter. Eacli thus becomes in turn the controlling area. 

Tlie Australian monsoons, however^ do not compare in regularity with those 
of India. 

Over the Gulf of Guinea and the Mediterranean periodical winds blow in 
summer in opposite directions ; the winds of the Gulf of Guinea come from the 
southwest, tliose of the Mediterranean — -known to the ancient Greeks as the 
Etesian winds — are from the northeast. Both are due to one cause, namely, 
the intense heating of the Sahara. This produces an upward current of lieated 
air and an inrush of cooler air from the Gulf of Guinea on the one side, and 
from the Mediterranean on the other. 

The periodical winds of Mexico, Central America, and the Brazilian waters, 
and those known in Texas as " Northers," are due to causes similar to those 
of the monsoons. 

Among the periodic winds of less importance are the return 
currents from deserts. These are laden with heat, sand, and 
dust. 

From the Sahara currents flow northward and southward. Those from 
the soutli enter Egypt, and blow for a few days at a time during a period of 
50 days. Hence they are called khamsin^ an Arabic word meaning fifty. 
During their prevalence the air is filled with blinding dust and the midday sun 
is darkened. By such a wind of unusual violence, the army of Cambyses, 
50.000 in number, is said to have been destroyed, when on its way to attack 
the oasis and temple of Jupiter Ammon. 

Crossing the Mediterranean, the desert wind scorches the vegetation of 
southern Europe. It is known as the sirocco. 

The tops of mountains chill the surrounding air. This some- 
times descends as a cold wind into the warmer regions below. 
Thus from the snowy heights of the Andes the cold pamperos 
sweep over the Pampas of the Rio Plata, the icy p?nia descends 
upon the table-land of Peru, and the chilling mistral descends 
from the Alps to the shores of the Mediterranean, causing great 
discomfort to sick and well. 



SURFACE EFFECTS OF WINDS 



22,'J 



Surface Effects of 
Winds are especially 
well shown along 
sandy coasts and in 
arid regions. By the 
constant blowing of 
the wind sand is ac- 
cumulated in rounded 
ridges, like snowdrifts, 
called dunes. These 
heaps are by no means 
stationary, but advance 
with the wind, some- 
times overwhelming 
forests and converting arable lands into barren wastes. Large 
dunes are found on the southwest coast of France. Here for 



■Hfi^..:.--.' . * ..-*ei^MK* 




;^«-::-:i^?^^^^S:;:^|| 


T- 


R^ 





Sand Dune at Dune Park, Indiana 

Showing the general level surface and the steep lee 

slope encroaching on a pine forest. 




Surface or Dune, Dune 1'ai;k, I.mjiana 
Showing the destruction of a forest by dune invasion. (From United States Geological 

Survey.) 



228 ATMOSPHERIC CIRCULATION 

the distance of 150 miles they cover a strip several miles v^ide, 
attaining in some instances the height of 300 feet. At the head 
of Lake Michigan and on its eastern shore are found large 
dunes. On the Pacific coast, near the Golden Gate and else- 
where, the drifting of the sand has been prevented by the culti- 
vation of certain plants. The heaping up of sand ridges in 
desert regions through wind action is also common, as in Africa, 
Arabia, and the Great Basin. Moreover, blowing sand is an 
agent of abrasion and by it even rocks are worn away. 

Among other surface effects of wind mention may be made of 
the stripping of land surfaces, the transportation of dust, and the 
destruction of forests. 



XXI. STORMS 

General Description. — Storms and tempests are sudden and 
violent disturbances of the atmosphere. At sea they are among 
tlie most grand and terribly sublime spectacles in nature. A 
wind becomes a storm when it attains the velocity of 50 miles 
or more an hour. 

The great storms of the West Indies and of the Indian Ocean 
are called hurricanes ; those of the China Sea, typhoons. These 
storms, which are alike in cause and character, together with the 
great eastward-moving swirls of the temperate regions, may be 
considered under the general name of cyclone. This word, de- 
rived from the Greek kiiklos, circle, refers to the fact that they 
consist of columns of air revolving round a perpendicular axis. 





Sketch TO ILLUSTRATE THE Lower-atmospheric Circulation in a Hurricane 
The inward spiral at the base is the surface wind. (After Everett Hayden in Natioital 
Geographical Magazine?) 



At the same time they have a progressive motion of greater or 
less rapidity over a certain portion of the surface of the earth. 

Cause of Storms. — The general cause of all such atr^ospheric 
disturbances is the same in principle as that of ordinary winds. 

229 



230 



STORMS 



COURSE OF CYCLONE 
Northern Hemisphere 



It is a difference or inequality of pressure or weight, in different 
regions of the atmosphere. The principle may be thus stated : 
Into an area of low barometer a wind must always blow from an 
area of high barometer. 

When from any cause the weight of the atmosphere in a locality 

is diminished, an 
ascending current 
results. Currents 
of colder and 
heavier air rush 
in to supply the 
deficiency. The 
force and velocity 
of the currents 
thus created will be 
greater or less ac- 
cording to the dif- 
ference of atmos- 
pheric pressure, 
or the "gradient," 
as meteorologists 
call this differ- 
ence. The larger 
the gradient, the 
more violent will 
be the resulting 
wind. 

Suppose there 
is but one area of 
low barometer and 
one of high ; the 
result will be a 
simple wind moving in one direction. If, however, the one 
area of low barometer is surrounded by areas of high barometer, 
it is evident that there will be an inflow of air from all directions. 
Such currents do not collide at the center, but, in obedience to 




^^^^ 



COURSEOF CYCLONE 
Southern Hemisphere 



Course of Cyclones 




LAWS OF STORMS 



231 



a force arising from the 
earth's rotation, are de- 
flected to the right in 
the northern hemisphere 
and to the left in the 
southern.^ They there- 
fore circle round this 
area, thus forming a cy- 
clone. The course of 
the atmospheric currents 
during a disturbance of 
this kind is shown in the 
diagram on p. 229. 

Laws of Storms. — 
Cyclones obey the fol- 
lowing laws: — 

(i) The wind revolves 
in opposite directions 
according as the cyclone 
is in the northern or 
southern hemisphere. In 
the northern the direc- 
tion of revolution is from 
right to left, or against 
the hands of a watch. 
In the southern it is 
from left to right, or with 
the hands of a watch. 

As the wind constantly re- 
volves, it constantly changes 
its direction at any given place 
in the storm track. On oppo- 
site sides of the center it has 
opposite directions. Hence 
it is easy to understand why 

M.-S. PHYS. GEOG. — I4 



NORTHERN HEMISPHERE 

V/ind East 




Wind East 

Storm Cards 
Showing direction of whirl in both hemispheres. 

1 Ferrel's law. 



232 STORMS 

the wind changes as soon as the storm' center passes. This is shown by the 
" storm cards." 

The rate of revolution, or "velocity of the wind," is from 50 to 150 miles 
an hour. 

(2) The storm, while revolving, has a progressive motion. 
The direction of this motion is determined by the prevailing 
winds. In general it is northwest and southwest within the 
zones of the trades, and northeast and southeast in those of the 
counter trades. 

The course of tropical cyclones is well defined. North of the 
equator they move northwestwardly up to about latitude 30° N. 
Here they turn to the northeast. South of the equator they 
pursue the reverse course ; starting near the tropics, they advance 
toward the southwest, and near the parallel or 27° they turn to 
the southeast. From this it will be seen that the pathway of 
cyclones somewhat resembles the curve called ^.parabola. (See 
diagram, p. 230.) The rate of travel varies from i to 70 miles 
an hour. 

(3) The storm center is an area of calm and also of low 
barometer. The arrival of the storm center at any point is 
indicated by the barometer. The descent of the mercury in 
tropical storms often amounts to two inches. It is sometimes 
so rapid that it can be detected by the eye. 

This fall of the barometer occurs at the storm center for two 
reasons : ist, because the center is an area of warm, humid air; 
2d, because the center is an area of rarefaction. 

The air particles which are nearest the vertical center of the cyclone are 
apparently repelled outward from that center by their centrifugal force. 
This makes the air in the center less dense, or, as we commonly say, rare- 
fies it. Sometimes it would seem that the rarefaction almost amounts to a 
vacuum. 

Anti-cyclones. — Closely associated with cyclones are vast 
bodies of air the condition of which is the reverse of that of the 
cyclone. To such bodies of air is given the name anti-cyclone; 
that is, opposite of the cyclone. 

The cyclone is warm, moist, and light. The anti-cyclone is 



VALUE OF STORM LAWS 233 

cold, dry, and heavy. Hence the area over which an anti- 
cyclone prevails is one of high barometer. Occasionally in an 
anti-cyclone the mercury will rise to 31.25 inches. 

Again, while in a cyclone air currents flow inward from the 
circumference toward the center, in the anti-cyclone currents 
flow outward from the center toward the circumference. 

Value of Storm Laws. — A knowledge of the laws of storms 
is of the utmost value to the navigator. By observing the 
direction of the wind he may learn in what direction the storm 
center is from him. The rule is : Turn your back to the wind 
and the low barometer is always to your left in the northern 
hemisphere, and in the southern hemisphere to your right. This 
will appear by examining the diagram on page 230, and imagin- 
ing yourself with your back to the arrowheads. If the sailor 
knows where the storm center is, he can steer away from it. 

Again, if he finds his barometer sinking rapidly, an inch or 
more below its usual height, he knows that he is in the storm 
center. Obviously it will be well to trim the sails and prepare 
for a gale. The center of calm will soon pass beyond and a 
tempest strike his ship. 

The Areas of Storms differ in size and shape. In Europe 
they are nearly circular ; in the United States, their shape is 
usually an elongated oval. They are seldom less than 600 
miles in diameter. They average twice that amount. 

Tornadoes and Whirlwinds differ from hurricanes and ty- 
phoons, (i) in duration ; and (2) in extent of area. 

In passing over any point, tornadoes seldom occupy more 
than a few seconds. Their breadth varies from a few yards to 
a mile or two, though their destructive effects are usually con- 
fined to a narrow path. 

The rate of their progressive motion is commonly about 30 
miles an hour, and the length of their course 25 or 30 miles. 

An approaching tornado has the form of a funnel-shaped 
cloud pointing downward. A noise, perhaps due to electricity, 
and not unlike that of a train of cars, is heard ; thunder, light- 
ning, hail, and rain occur. 



234 



STORMS 



A partial vacuum is formed by the centrifugal force at the 
center. Sometimes when the end of the funnel dips down and 
touches a building, the vacuum resting over it so relieves the 
building from atmospheric pressure as to cause a sudden expan- 
sion of the air con- 
tained in it. The walls 
cf the building then 
burst asunder as by 
explosive force. 

Tornadoes sweep 
everything before 
them. Houses and 
other buildings are 
lifted up bodily, and 
lanes called "wind 
roads " are cut 
through the forests. 
Large trees are up- 
rooted and whirled 
about like stubble. 

The region of 
North America most 
frequently visited by 
tornadoes is the Mis- 
sissippi Valley. Dur- 
ing the past 50 years 
more than 600 have 
occurred there. 

In the deserts of 
Asia and Africa, as 
well as in the region 
of the Great Basin of North America, whirlwinds sometimes 
draw up into their central core large quantities of sand and dust. 
They thus become moving columns of sand, 500 to 700 feet in 
height (as observed with sextant), and are known as "dust 
whirlwinds." 




A TORXADU 

The tornado here shown is from a photograph taken by 
Mr. W. E. Seright at Stafford, Kansas, about 5 : 30 
P.M., April 12, 1906. It was the last of six or seven 
similar manifestations which occurred within the 
radius of three or four miles the same afternoon. 
When photographed the cloud was probably a mile 
distant in a northeast direction. 



DISTRIBUTION OF STORMS 



235 



The Simoovi, or "poison wind," appears to be a desert whirl- 
wind intensely hot, and so rarefied as to be suffocating. 

At sea, especially in cer- 
tain parts of the ocean, 
waterspouts occur. These 
are tall moving columns 
of water. Scientific opinion 
is divided as to their cause. 
Some think that they are 
produced like the dust 
whirlwinds of the desert, 
by a revolving air current 
which draws up the spray 
of the waves into its core 
of low pressure. Others 
think that the water comes 
solely from the clouds. 
The cut seems to suggest 
the* latter view. Two 
actual, careful observers of 
the spout photographed 
drew, however, opposite 
conclusions from their 
observations. 

Distribution of Storms. — 
The most violent storms 
occur in the vicinity of 
mountainous islands. 

The Pacific is the most 
tranquil of the oceans. In 
those portions of its trade- 
wind regions where there 
are no islands, and where 

monsoons do not prevail, storms are almost unknown. The 
typhoons are confined to the southeast coasts of Asia and the 
East India Archipelago. 




Waterspout as seen from Oak Bluffs 
(Cottage City), Mass., August 19, 1896, 

AT 1 : 02 P.M. 




2.^6 



WEATHER FORECASTS 237 

The South Atlantic, along the coast of intertropical Brazil, 
is almost stormless, whereas, in corresponding latitudes in the 
North Atlantic, among the West Indies, terrific hurricanes 
occur. 

The portions of the Indian Ocean especially subject to 
hurricanes are the Bay of Bengal and the neighborhood of 
Mauritius. 

Weather Forecasts.^ — During the last 50 years observa- 
tions upon the force and direction of the wind, the course 
and character of storms, the pressure of the atmosphere, the 
amount of rainfall, the temperature and moisture of the air, 
have disclosed certain general principles or laws of the weatjier. 

Knowing these laws, and knowing by telegraphic reports 
the weather conditions prevailing throughout the country, it 
is possible to predict from day to day, with considerable accu- 
racy, the approach of storms, or of cold or hot weather. 

Most of the great storms of the United States travel in a 
northeasterly direction. They may be conveniently classed as 
those which come from the Pacific Ocean and those which 
come from the Atlantic. 

The storms of the Pacific penetrate to a greater or less dis- 
tance into the country, and often cross it entirely. 

The storms from the Atlantic are first felt either at some 
southerly point on the Atlantic seaboard, or on the shores of 
the Gulf. Generally they come in from sea by the way of the 
Gulf, pass northward through the Mississippi Valley, and then 
turn to the northeast. 

1 Over 50 years ago Maury urged upon the attention of the government of the 
United States, and those of European nations, the desirability of having systematic 
meteorological observations carried on by all nations at sea. As the result of his 
efforts the United States government invited all the maritime states of Christendom 
to a conference, which took place in Brussels, 1853. The suggestions made were 
adopted. But the ideas of Maury were not limited to the ocean. In the preface to 
the second edition of his' " Physical Geography of the Sea," published in 1855, he 
says : "It is a pity that the system of observations recommended by the conference 
should relate only to the sea. The plan should include the land also, and be uni- 
versal." The present " U. S. Weather Bureau " with its well-organized, Signal 
Service is the crowning result of his labors in this direction. 



238 STORMS 

Those which make their appearance first on the Atlantic seaboard are the 
western halves of cyclones, which, pursuing their parabolic course, first north- 
westwardly and then northeastwardly, happen partially to embrace our shores 
within their area. These western half-cyclones consist of northeast and 
northwest gales. The eastern halves of the same storms, consisting of gales 
from the southwest and southeast, are at sea. The storm center pursues a 
course nearly coinciding with our shore line. 

The transient and uncertain character of tornadoes renders it 
impossible to make exact predictions regarding them. 

Ordinary storms, however, are so far regular that, in a large 
proportion of cases, their course, after they have once manifested 
themselves, may be foretold with some degree of accuracy. 

Xjae Weather Map. — The following description of the 
Weather Map is taken from a pubHcation b}^ the Chief of 
the United States Weather Bureau (see map, p. 236): "This 
map presents an outline of the United States and Canada, and 
shows stations where weather observations are taken daily at 
8 A.M. and 8 p.m., seventy-fifth meridian time. These obser- 
vations consist of readings of the barometer, thermometer (dry 
and wet), direction and velocity of the wind, state of weather, 
amount, kind, and direction of the clouds, and amount of rain 
or snow, and are telegraphed to Washington and to many of 
the Weather Bureau stations throughout the country for publi- 
cation on maps and bulletins. Solid lines, called isobars, are 
drawn through points having the same atmospheric pressure ; 
a separate line being drawn for each one tenth of an inch in 
the height of the barometer. Dotted lines, called isotherms, 
connecting places having the same temperature, are drawn for 
each 10 degrees of the thermometer. Heavy dotted lines, 
inclosing areas where a decided change of temperature has 
occurred within the last 24 hours, are sometimes added. The 
direction of the wind is indicated by an arrow flying with 
the wind, or opposite to the ordinary vane. The state of 
the weather — whether clear, partly cloudy, cloudy, raining, or 
snowing — is indicated by the circular symbol. Shaded areas, 
when used, show where rain or snow has fallen since the last 
observation." 



XXII. MOISTURE OF THE AIR 

Humidity. — More or less moisture is always present in the 
air. It exists as vapor. This vapor is invisible, yet its presence 
is often recognized by the sensation of dampness. The amount 
of vapor in the air is greater over the sea and other large bodies 
of water than over the land. It is dissipated by heat and con- 
densed by cold. In arid regions the moisture available is less 
than the capacity of the air to hold, hence the air is dry. The 
presence or absence of moisture in the atmosphere has a marked 
effect on climate. Great humidity is enervating and not con- 
ducive to mental or physical exertion ; temperature sensations 
are exaggerated ; human activities curtailed. Dry air, on the 
contrary, is bracing, and higher temperatures can be endured 
without discomfort. 

Evaporation. — One of the most remarable properties of water 
is the readiness with which it passes from one of its forms to 
another. Whenever it assumes the form of vapor it is said to 
evaporate, and the process of evaporation goes on at all tempera- 
tures and vmder all circumstances until the air is saturated. 
When the point of saturation has been reached, it can hold no 
more moisture. 

You may have observed water drying in the streets and roads after a rain, 
or clothe^ hanging on the line frozen stiff, and yet becoming dry ; or you may 
have seen a light fall of snow disappear in freezing weather. These were cases 
of evaporation. 

Evaporation is accelerated and increased under the following 
conditions : — 

(i) By high temperature. From this it follows that the maxi- 
mum of evaporation is found within the tropics ; the minimum 
at the poles. Furthermore, that evaporation takes place during 
the day, and in the warmest part of the day. 

239 



240 MOISTURE OF THE AIR 

(2) By diminution of pressure. In a vacuum there is almost 
no pressure, and there evaporation taices place almost instan- 
taneously. Hence on the tops of high mountains, where the 
pressure of the atmosphere is very much diminished, evaporation 
goes on much more rapidly than it does at the sea level, where 
the full pressure of the entire atmosphere is felt. 

Indeed, mountain peaks may be so high as to be entirely free 
from snow, while a belt of snow girdles the lower part of the 
mountain. The reason of this appears to be that at certain alti- 
tudes and under certain conditions snow evaporates so rapidly 
that it cannot accumulate. 

Aconcagua in Chile sometimes appears with its bare and bleak 
top peering above a girdle of snow. 

(3) By a dry condition of the atmosphere. Warm dry air will 
absorb far more moisture than that which is cool and damp. 
If air be near the point of saturation, it is clear that evaporation 
will be retarded ; but if the air be dry, it will be accelerated. 

(4) By wind. If a wind blows upon the surface of water, 
evaporation is accelerated. As fast as one portion of the air be- 
comes charged with vapor, it is removed, and a fresh portion 
takes its place. 

Condensation and Precipitation. — Vapor returns to the 
liquid or solid state and is deposited upon the earth by the pro- 
cesses called condensation and precipitation. 

When condensed, it assumes the form of dew, white or hoar- 
frost, fog or cloud, hail or snow. 

The great cause of precipitation, or the removal of moisture 
from the atmosphere, is loss of heat. The atmosphere can 
contain more or less vapor in a state of absorption in proportion 
to its temperature. If the temperature is 50°, a cubic foot of air 
can absorb about two grains' weight of vapor. At the tempera- 
ture of 70°, that is, with an increase of only 20° of heat, the 
proportion of vapor is about twice as great. 

From this it is easy to see why reduction of temperature causes 
precipitation. Suppose a cubic foot of air saturated with mois- 
ture to be reduced in temperature, even very slightly ; it is ob- 



HOW DEW IS FORMED 



241 



vious that its capacity for moisture will be at once reduced, 
and a certain portion of its vapor must be precipitated. The 
temperature at which the deposit in such cases begins to take 
place is called the dew-point. 

How Dew is Formed. — On clear and calm nights, the grass, 
the leaves, and other objects rapidly radiate their heat and grow 




Cirrus Streamers with Low Cumulus on the Horizon, Washington, D.C 
From photograph by Professor A. J. Henry. 

cool. They chill the surrounding air. It can no longer contain 
the same amount of moisture as when it was warm. Hence a 
portion of it is condensed and deposited upon the leaves in the 
shape of fine drops of water. We often say " the dew begins to 
fall,'' though, strictly speaking, it does not fall. It is deposited 
upon the grass precisely as, on a hot summer's day, the moisture 
is deposited on the outside of a pitcher of ice water. 

Clouds check radiation, and hence on cloudy nights less dew, 
or perhaps none at all, is deposited. 

You must have noticed that dew and hoar frost, which is the 



242 



MOISTURE OF THE AIR 



same as dew, only frozen, are deposited on some objects more 
copiously than others. This is because some radiate heat more 
rapidly, and therefore chill and condense more quickly the vapor 
that floats above them. 

Fog. — Vapor coming in contact with cool air, if chilled below 




Cirrus Cloud merging into Cirro-stratus, Washington, D.C. 
From photograph by Professor A. J. Henry. 

the dew-point, assumes the form of fine watery particles which 
we call mist ox fog. 

It may also have been observed that in a clear, calm, and 
frosty morning the springs, ponds, and rivers " smoke." This 
phenomenon is identical with that exhibited by the steam which 
issues from the teakettle, the locomotive, and the steamboat. 
The " smoke " is a miniature fog. 

Often, too, fogs are seen upon the surface of rivers in early 
morning which vanish before noon. The morning air, being 



CLOUDS 



243 



cool, cannot absorb this moisture, but later in the day when its 
capacity has been increased by warming, it readily absorbs the 
fog. 

Tlie most foggy sea in the world is that part of the North Atlantic Ocean that 
lies on the polar side of latitude 40''; and the most foggy place is on the 
Grand Banks of Newfoundland. 




DOUBLE-TURRETED CUMULUS, LOWER POTOMAC RiVER 
From photograph by Professor A. J. Henry. 

Vapor rises rapidly from the warm water of the Gulf Stream. Near the 
Grand Banks the Gulf Stream meets the icy Labrador Current. Owing to the 
chilling influence of this current, the vapor is condensed into fog as fast as it 
rises. 

Though fogs are most frequent in summer, they occur on the Grand Banks 
at all seasons, producing in winter the exquisitely beautiful silver fogs of New- 
foundland, which garnish the forests of that island with frostwork. 

Clouds. — A cloud is simply a mass of mist or fog floating 
high in the air instead of near the ground. 



244 



MOISTURE OF THE AIR 



Clouds present a very great variety of appearance, and hence 
are divided into seven classes : three simple, cirnts, ciinmlus, and 
stratus ; four compound, cirfo-cumnbis, cirro-strat7is, cimmlo- 
stratus, and cumiilo-cirro-stratus or nimbus. 

The cirrus or curl cloud consists of white wavy lines or curled 






ClKROCUMULU'S CLOUD, "MACKEREL SKY," WASHINGTON, D.C. 

From photograph by Professor A. J. Henry. 

bands. It is the hghtest of all cloud forms, and attains the 
highest elevations, floating four or five miles above the surface 
of the earth in regions of perpetual frost. It is supposed to 
consist of minute crystals of ice such as we see in the snowflake, 
and may be defined as frozen fog. 

Cirrus clouds are often heralds of the cyclone. These nimble forerunners 
have been observed 800 miles in advance of a storm. They sometimes cau- 
tion the mariner, before his barometer gives any intimation of the approaching 
tempest. 



CLOUDS 245 

Cumulus clouds derive their name from the fact that they are 
heaped up, like vast mountains towering one upon another. 
They are often of glistening whiteness. They abound in the 
tropics, and frequently appear in the sky of temperate latitudes 
during the summer, when evaporation is rapid. 

Of all cloud forms they are perhaps the grandest. Out of 




CUMULO-STRATUS, KNOXVILLE, TENN. 

them darts the lightning which makes our thunder storms so 
magnificent. 

Stratus clouds appear in the shape of long layers or ribbons. 
They are seen most frequently in the evening, and, when tinged 
by the rays of the setting sun, they form those islets of gold 
which render the sunset sky so beautiful. 

The compound clouds combine the features of the simple 
ones from which they are named. 

The Cirro-cumulus is made up of fleecy masses of cirrus which 
roll themselves up into rounded shapes. These cause the 
mottled appearance commonly known as a "mackerel sky." 



246 MOISTURE OF THE AIR 

The Cirro-stratus consists of layers of cirrus clouds. They 
are often so arranged as to resemble a shoal of fishes, all swim- 
ming parallel to one another. This cloud, like the cirrus, is 
often the precursor of storms. 

The Cumulo-stratus is formed of heaped clouds resting on 
layer clouds. Like the cumulus, its general mass is often quite 




Cumulus and Nimbus, Seascai'f, 
(United States Weather Bureau.) 

dark and threatening, while its edges are bright with sunshine 
that is behind the clouds. 

The Nimbus is simply a cloud of any kind from which rain 
falls. Heaped clouds, and curls and layers blend together, lose 
their characteristic features, and form one dense leaden mass. 
It often overspreads the whole heavens. 

When clouds rest on the tops of mountains, they are actually 
in contact with the earth ; often indeed they are below the sum- 
mit of the mountain. Their average elevation, however, is about 
half a mile. At times they cannot be less than four or five 
miles high. 



CLOUDS 247 

The velocity of cloud movement, when accurately estimated 
by observers, is found to be far more rapid than we should sup- 
pose from the apparent rate of the "passing cloud." It has 
been found that cirro-cumulus and cirrus clouds which seem 
to be moving at a leisurely rate are often traveling 75 to 100 
miles an hour. 

This is of very great interest, for it indicates to us the velocity 
of the upper currents of the atmosphere. 

Clouds screen the earth from excessive heat in summer, while 
as a mantle they keep it warm in winter by checking radiation. 

Plants and animals are distressed by the intense heat of the noonday sun. 
But the more powerful the ray, the more rapid is evaporation. Soon vapor 
enough is Hfted from the- earth to form the mitigating clouds. They over- 
shadow the land, and plants and animals rejoice in their shelter. 



M.-S. PHYS. GEOG. — 1 5 



XXIII. RAIN 

General Statement. — The first form assumed by the moisture 
of the upper air when condensed is that of cloud. If, however, 
the process of condensation continues, and vapor exists in abun- 
dance, it is easy to see that the tiny water particles which make 
up the cloud will increase in size, until they are too heavy to 
float, and will fall as raindrops to the earth. 

The general cause of rainfall is that a certain volume of vapor- 
laden air has been chilled below the dew-point, so that it has no 
longer the same capacity for moisture as before. This may be 
brought about in several ways : (i) The moist air maybe driven 
up a lofty mountain slope into the higher and colder regions of 
the atmosphere; (2) it may be carried upward as an ascending 
current of heated air ; (3) it may be chilled by being mixed with 
a mass of colder air ; (4) it may be chilled by being expanded, 
when drawn into the center of a cyclone. Such a center is an 
area of rarefaction. Hence air entering it will expand, and 
expansion has the effect of cooling it and condensing its vapor. 
This last cause produces the heaviest rainfalls for short periods. 

Distribution of Rain. — Rain is very unequally distributed over 
the earth. 

(i) The rainfall is greater on land than at sea. 

(2) It is greater in mountainous than in level regions. 

The reason of both these facts is, that elevations have the 
effect of directing vapor-laden air into the higher, cooler regions 
of the atmosphere. 

(3) The rainfall is greater in the torrid than in any other 
zone. The average annual quantity at the equator is eight feet. 
It diminishes as we approach the poles. This follows from the 
fact that the torrid zone, being the hottest, is that of the greatest 
evaporation. 

249 



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REGULATORS OF RAINFALL 25 1 

These are the general facts regarding the distribution of rain. 
We must now consider more in detail how this distribution is 
brought about. 

Regulators of Rainfall. — The great regulators of rainfall are 
mountains, deserts, and winds. Each of these has an important 
part to perform in the distribution of rain over the surface of 
the earth. 

Mountains are the great condensers of vapor. If mountain 
chains face winds coming from the sea, the land lying between 
them and the sea is well watered. As they rob the winds of 
their moisture, not unfrequently the region lying beyond them is 
rainless. 

Thus the Himalayas face the southwest monsoon, as it comes 
freighted with vapor from the Indian Ocean. They make 
India one of the most productive countries in the world ; but 
the plateaus lying to the north of them are almost rainless. On 
a smaller scale the Western Ghauts act in the same way. They, 
too, lie in the pathway of the monsoons, and intercept and con- 
dense their vapors. The annual rainfall upon their tops 
amounts to about 260 inches, while the country on the east of 
them receives less than 30 inches. 

But perhaps the most striking illustration of the influence of 
mountains upon rainfall is to be found in the case of the Khasia 
hills, on the northern shores of the Bay of Bengal. They in- 
tercept the southwest monsoons, as they come burdened with 
vapor from the bay. The result is that the winds, as they slant 
up the hills into the higher and cooler air, have their moisture 
at once precipitated as rain, of which about 500 inches fall there 
in the year. 

In South America the influence of the Andes is famihar. 
The northeast and southeast trades come from the sea saturated 
with vapor, and so go into the interior, rising, and cooling, and. 
dispensing showers as they go, until they reach the crest of the 
Andes. Here the cold is sufficient to precipitate almost all the 
remaining moisture. Thus the eastern side of these mountains, 
within the trade-wind region (see Chart of the Winds), is abun- 



252 



RAIN 



dantly watered, while the western is dry. Hence it is that Peru 
is a rainless country. 

South of the mouth of the Plata, the reverse takes place. 
There the prevailing winds are from the west. They come from 
the Pacific, reeking with moisture, and water the western slopes 
of the Andes, causing the excessive rains of southern Chile, 
while the eastern slopes are comparatively dry. 

In our own country the Cascade Range and the Sierra 
Nevada have a similar influence. They lie in the pathway of 
the westerly winds which come loaded with moisture from the 
Pacific. They act as condensers, and bring down the copious 
showers which give fertihty to the Pacific slope. 

In mountainless areas, like the Dakotas, rain and snow are caused by 
currents of cold air descending from the upper regions of the atmosphere. 
They reduce the temperature with surprising rapidity. Pouring into a ■warm 
atmosphere, they condense its moisture, and a rainfall or snowfall is the 
result. 

In many cases deserts are the directors of the winds, and 
thus become regulators of the rainfall. 

India is in a region in which the northeast trade winds blow 
over the land and are rainless. Were it not for the deserts of 
central Asia, which have the effect of drawing in the southwest 
monsoons (see p. 224), India would be as arid as Gobi. 

In Africa the Sahara produces the monsoons which blow from 
the Indian Ocean upon that continent. By June, the desert is 
heated sufficiently to bring in the sea winds. The rainy season 
then begins, and lasts till late in autumn. 

The periodical overflow of the Nile is due to rain resulting 
from the condensation of vapor brought from the sea by the 
African monsoon. Thus Egypt owes it fertility in some degree 
to the burning sands of the Sahara. 

North America has its deserts and its monsoons, though they 
are far less marked than those of the Old World. 

The table-lands of Mexico, Arizona, the dry plains of Texas, New Mexico, 
and the neighboring regions, are heated by the summer sun to such a degree, 
that the air resting upon them becomes rarefied, and ascends, the cooler air 



RAINS CLASSIFIED 253 

from far and near coming in to restore the equilibrium. Thus a southeast 
monsoon is created in the Gulf of Mexico, and a southwest one in the Pacific. 
Both of these winds blow toward the land, and bring the rains to Mexico, 
so that one side of that country is watered from the Pacific, and the other 
from the Atlantic Ocean. 

As a general rule winds are dry, if they have traversed the 
land or if they are journeying toward the equator. Winds are 
wet, if they have traversed the sea or if they are journeying 
from the equator. 

Land winds are dry for the simple reason that they have so 
little opportunity to take up moisture. Thus the northeast 
monsoons which sweep over the inland regions of Asia are the 
dry monsoons. The westerly winds of our own country, from 
the Sierra Nevada to the Atlantic, are dry winds. They bring 
our fair weather. 

Again, a wind that is blowing toward the equator is dry, 
because, entering warmer latitudes, it is gaining capacity for 
moisture with every degree of its progress. The trade winds, 
for example, blow toward the equator. You perceive, therefore, 
that they are going from cooler to warmer latitudes. Their 
temperature is increased by the way, and with increase^ of 
temperature there is increase of capacity for moisture. The 
trade winds, therefore, take up more water from the sea than 
they return to it. They are evaporating winds. 

Sea winds and winds blowing toward the poles arc rainy. 
The counter trades go toward the poles. They are traveling 
from warmer to cooler latitudes. Their temperature is de- 
creased by the way, and therefore there is a decrease in their 
capacity for moisture ; they deposit more than they take up. 
They are, therefore, rain winds. 

Rains Classified. — The winds are classified according to the 
regularity with which they blow, as constant, variable, and 
periodical. It is proper, therefore, to classify the rains which 
they bring in the same way. Hence, according to the nature 
of the supplying winds, the rainfall in any given region is con- 
stant, periodical, or variable. 



254 ^^iN 

The constant rains are confined to a belt near the equator, 
about 5° wide. In this belt there are almost daily showers. 
The cause is clear. The northeast and southeast trades meet 
near the equator. They are so completely saturated with 
moisture that the sailor, hanging out his clothes in the morn- 
ing, is often surprised to find in the evening that they have not 
dried in the least. Under the vertical rays of the sun an as- 
cending current is produced which carries the vapor-laden air 
into the higher regions of the atmosphere. Here the vapor is 
cooled and condensed ; and hence the frequent thunder showers 
of this region of constant precipitation. 

Within the tropics, to the north and to the south of the 
narrow belt of Constant Rains, lie the zones of Periodical 
Rains. 

In the New World the periodical rainfall is closely connected 
with the annual movement of the Equatorial Calm Belt and its 
accompanying Cloud Ring. 

The Calm Belt travels northward and southward, following 
the annual movement of the sun in the heavens. It is farthest 
south in March, and farthest north in September. 

During the time that it is passing over a place, it gives to that 
place its rainy season. After it has passed, there is scarcely 
a drop of rain until it comes again. 

Let us follow the Cloud Ring in its journey from south to north, and we 
shall readily understand its movements, and the rainy seasons that depend 
upon them. 

The time is February; it is then over Guayaquil (Lat. 3° S.), and then the 
rainy season there is at its height. It commences its movement for the north 
in March. Quitting the skies of Guayaquil soon after, it leaves them bright 
and clear with the commencement of the dry season. In a little while it has 
traveled as far as latitude 4° N. It then overshadows Bogota, where the rains 
begin in April or May. In June it is over Panama, and hence a rainy season 
prevails there ; and so the Cloud Ring continues on to Mexico, reaching 
Mazatlan, just under the tropic, about September, when it commences its 
march toward the south, so as to be again at Guayaquil by February or 
March. 

It is clear that on its return from north to south the Cloud Ring must give 



EXCESSIVE AND DEFICIENT RAINFALL 255 

to certain places a second rainy season because, in coming and going, it 
passes over tliem twice. 

In the Old World the periodical rains are occasioned by the 
monsoons or reversed trades. For about six months, in south- 
ern Asia and central Africa, copious rains fall. When the mon- 
soons change, the dry season sets in, and scarcely any rain falls 
until after six months, when the wet monsoon begins to blow 
again. 

Within the two belts of Periodical Rains the year is divided 
into rainy seasons and dry. 

In general terms, the rainy season in the northern belt may be said to begin 
with April and last till October, while the dry season extends from October 
till April. In the southern belt this order is reversed — the dry season lasting 
from April till October, and the season of rain from October till April. 

It is not to be supposed that during the rainy season there is an incessant 
fall of rain. In Mexico, for instance, the rainy season is the most delightful 
portion of the year. As a rule the nights and mornings are clear and beautiful, 
and the weather fine, with a few hours of rain after three or four o'clock p.m. 

North and south of the belts of Periodi-cal Rains, the rains 
become variable ; that is, they are irregularly distributed through 
the year. In some countries they occur mainly during the sum- 
mer, in others during the winter; in others, again, during the 
spring and autumn. This condition prevails throughout the 
temperate regions. 

Excessive and Deficient Rainfall. — Owing to the influence of 
local causes, there are regions of excessive and deficient rainfall. 

The regions of excessive rainfall, with few exceptions, lie 
within or near the tropics. Cherrapunjee, in the vicinity of the 
Khasia hills in India, receives annually about 500, and in some 
years 600, inches — or a depth of 50 feet — a greater amount, 
so far as we know, than any other place on the globe. 

Parts of the British Isles, the coasts of Guinea and Senegambia, eastern 
Africa and India, are all remarkable for their heavy rainfall. 

In the New World, Brazil, Guiana, Venezuela, the West India Islands, 
Central America, Patagonia, and the Pacific shores of Alaska are all regions 
of excessive rainfall. 



256 



RAIN 




The Primitive Method of Irrigation practiced by the Egyptian Peasants 

The water is raised in vessels attached to " sweeps " with counter weights at the opposite 

ends. 



EXCESSIVE AND DEFICIENT RAINFALL 257 

The rainless or almost rainless regions are the great belt of 
deserts extending across Africa and Asia, from the Atlantic 
nearly to the Pacific ; the Great Basin in North America, lying 
eastward of the Sierra Nevada ; Peru, together with the north- 
ern part of Chile, and portions of the Argentine Republic lying 
eastward of the Andes. 

Cultivation in ail dry countries is carried on by means of irrigation. For 
this purpose tanks have been constructed in India at vast expense. The Peru- 
vian farmers avail themselves of the mountain streams that are fed by the 
snows of the Andes ; while the peasant of. Egypt, like his forefathers, supplies 
his fields and gardens from the waters of the Nile. (For irrigation in United 
States, see p. 320.) 



XXIV. HAIL, SNOW, AND GLACIERS 

Hail. — Moisture, descending through the cold upper regions 
of the atmosphere, is sometimes frozen and becomes hail or 
snow. 

When examined carefully, hail has been often found to consist 
of concentric layers of ice, incasing one another like the layers 
of an onion. 

In size, hailstones vary. At times they are as large as mar- 
bles, or even hens' eggs, so that severe hailstorms may occasion 
very great damage to crops. 

The formation of hail is not well understood. The sudden 
ascent of moist air into the cold upper regions of the atmosphere 
is probably the most common cause of this phenomenon. 

Glaisher, in his balloon ascension, found the temperature, at 
the height of three miles, i8° F. ; at four, 8° ; at five, — 2°. The 
temperature at the surface was 59°. 

Snow. —The moisture that falls from the clouds, frozen in 
flakes, is called snow. When examined, it is usually found to 
consist of exquisitely formed crystals, which are generally in the 
shape of a six-pointed star. (See illustration.) 

Snow rarely occurs within the limits of about 30° north and 
south latitude, except on high mountain tops. It is naturally 
more abundant as we approach the poles. It is also in general 
more abundant where the climate is inland, than where it is 
maritime. Paris has, on an average, 12 snowy days in the 
year; St. Petersburg, 170. 

Snow is perpetual, however, even at the equator, upon all 
heights greater than about three miles above the sea level. The 
line above which snow is always found is called the snow line. 
It varies in altitude from many causes. 

258 



SNOW 



259 



Whatever tends to elevate the temperature of any locality 
tends also to elevate the snow hne. Hence a low snow line 
means a cold climate. While at the equator the snow line is 
16,000 feet high, at the Straits of Magellan it is only about 4000, 
and in Norway about 5000. 

The use of snow is twofold : (i) it protects the earth and the 
crops planted in late autumn from the intense cold and the 
injurious effects of frost. Sometimes there is a difference of 
40° between the temperature of the ground a little below the 
surface and that of the snow that covers it ; (2) falling in vast 




Snow Crystals 



quantities on the great mountain ranges, as the Himalayas, the 
Alps, and the Rocky Mountains, it serves as perpetual feeders 
of the rivers. 

The quantity of snow that falls on an extensive range of mountains, such 
as the Alps, is very great. Agassiz observed a fall of 57 feet in six- 
months at the Hospice of Grimsel, and observations during twelve years near 
the Pass of the Great Saint Bernard showed an annual snowfall varying 
from 12 to 44 feet. It has been estimated that the average annual 
snowfall on the Alps amounts to 60 feet, which is equivalent to six feet 
of water. 

A large part of the snow, as already stated, gradually melts and flows 



26o 



HAIL, SNOW, AND GLACIERS 



through the river courses to the sea. Other, though smaller portions, 
consolidated into ice, descend the mountain slopes into the valleys as 
glaciers. Frequently masses of snow are loosened from their beds and 
plunge dovi^n the steep declivities with frightful velocity, forming avalanches. 
Sometimes the echo of a loud word is enough to disturb an overhanging 
mass and hurl it into the valley below. 




'lia^i^^^^ 










Effects of an Avalanche 
A scene in the Selkirk Mountains of British Columbia. 



Many instances are on record of the appalling destruction wrought by this 
scourge of the Alps, whole villages having been overwhelmed and hundreds 
of lives destroyed by a single avalanche. Thick forests are the best protec- 
tion against danger from this source, and in former times the penalty of death 
has been adjudged against any who should destroy a single tree of the pro- 
tecting barrier. 



GLACIERS 



261 



Glaciers are vast masses of ice either spreading out over the 
surface, as in Greenland and the Antarctic regions, or fiUing 
valleys, as in the Alps and other snow-clad mountains. 




A Snow-clad Summit — Mont Blanc, "The Monarch of the Alps" 

This mountain has an altitude of 15,730 feet. In the foreground is seen the village of 
Chamounix. Note the glacier extending downward into the valley. 

In regions where the snowfall exceeds the loss by melting, 
the accumulated snow gradually becomes compacted by par- 
tial melting and by the pressure of its own weight. Moreover, 
that which occupies the higher levels gradually creeps down- 
ward to the lower — to the edge of the plateau in the case of 
an ice sheet, or down a valley in the case of a mountain 
glacier. 



262 



HAIL, SNOW, AND GLACIERS 



Should we follow a ravine downward from a snow-clad crest, 
we should find the snow growing more and more solid under 
our feet until we reached the snow line. Below this the com- 
pacted snow would appear as ice. Following the ravine to a 
still lower level, we should observe that the ice mass filled it 
from side to side and terminated at length among gardens 
and pastures, a stream of water gushing from its cavernous 
extremity. 

Other Glaciers, smaller in extent, and containing comparatively 
little ice, never reach the lower valleys. 




Mer de Glace — Sea of Ice 
This celebrated glacier is formed by the union of several branches descending from the 

Mont Blanc ra.ns'e. 



The compacted snow above the snow line is called the neve 
(na-va). The neve is in general about half the density of ice, 
or more than three times that of snow. 

Glacial Motion. — Solid and immovable as these mighty 
masses of ice appear, they are really in motion. Long before 
glacial motion was suspected by scientific men, it had been known 
to the mountaineers that blocks of stone lying upon the surface 
of glaciers moved slowly downward. 

A large number of carefully conducted observations have 



GLACIAL MOTION 



263 



been made, which prove not only that the glacier has motion, 
but that its motion closely resembles that of a river. It is 
swiftest in the center, and slower, owing to the friction, near 
the sides and bottom. Notwithstanding this movement, the 
termination of the glacier retains about the same position from 
year to year, because it is melted away as fast as it moves 
downward. 




Franz Josef Glacier, New Zealand 
This glacier lies on the western slope of the Southern Alps. Its length is 81/2 miles. 

The rapidity of the motion of a glacier depends upon the 
season of the year, the size of the glacier, and the incHnation 
of its bed. The motion is more rapid in summer than in win- 
ter, in the daytime than at night, and in a large and deep 
glacier than in a small one. 

The average rate per year for glaciers of the Alps varies 
from 25 to about lOO yards. 

The middle of the Mer de Glace was found by Tyndall to 

M.-S. PHYS. GEOG. — 1 6 



264 



HAIL, SNOW, AND GLACIERS 



move 20 to 33 inches a day in summer. The rate is about 
half as much in winter. 

The following figures express in yards the motion, during one year, 
of a row of poles set in a straight line across the glacier of the Aar, by 
Professor Agassiz : — 

5. 20. 48. 55. 62. 64. 67. 69. 79. 68. 64. 54. 47. 39. 21. II. I. 

The central part, therefore, moved about 80 yards a year. 

The great glaciers of Greenland and Alaska move at the 
rate of 60 to 100 feet a day. 

Some glaciers, notably that of the Rhone, tell their own tale 
of their movement down the valley. On their surface concen- 









The Muir Glacier, Alaska 
This great ice-stream, which results from the union of many tributaries, enters an inlet of 
the sea. Its water front is about a mile wide and rises perpendicularly 250 feet or 
more. From it masses of ice break away which float off as small icebergs. Since the 
above photograph was taken the extremity of the glacier is less accessible to tourists 
on account of the shoaling of the inlet. 



trie curves are seen bulging toward the lower end of the glacier. 
These show, as clearly as a line of stakes, the more rapid 
movement of the central portion of the glacier. 

Owing to the slowness of glacier motion, it may be a century 
or more before what is now the upper end of the glacier will 
get to the foot of the mountain. 

Theory of Glacial Motion. — Various theories, none of which 
is in all respects satisfactory, have been advanced to account 



THEORY OF GLACIAL MOTION 



265 



for glacial motion and the accompanying phenomena. The 
first thing to be accounted for is the motion itself. Two causes 
for this may be given : (i) gravitation ; (2) expansion within the 
glacier. It is probable that both these take part in producing 
the motion. 

Gravitation, or the weight of the glacier, would naturally 
draw the mass down the 
slopes of the valley. 

Expansion within the 
glacier needs explanation. 
When the water from the 
melted surface of the 
glacier percolates down- 
ward into the interior of 
the mass, it encounters a 
temperature of 32° F. It 
freezes and of course 
expands. Its expansion 
must necessarily take 
place in the direction of 
least resistance ; that is, 
toward the lower end of 
the valley. 

The following facts 
must now be considered : 
first, that the ice of a 
glacier accommodates it- 
self to the shape of its 
inclosing valley very much as a river does to its channel ; and, 
second, that after fracture its parts reunite. These phenomena 
are explained by what is known as regelation or second freezing. 
If we pound a mass of ice into fragments and then moisten 
the broken surfaces, the fragments will readily freeze compactly 
together again. 

This is what occurs in a glacier. In passing through narrow 
gorges it is crushed and broken, and in gliding over steep 




Crossing Franz Josef Glacier, New Zealand 
Note the irregularities of the surface in the form of 

pinnacles which have resulted from superficial 

meltins:. 



266 



HAIL, SNOW, AND GLACIERS 



- / /// 



?/*^~^,^^^_ 



/ 



Crevasses 



irregularities in its bed it is cracked and splintered. The lower 
parts break away from the upper, and fissures of great depth 

called crevasses are 
formed, as shown in 
the following illus- 
tration. 

But after the ice 
E has been thus 
r broken and splint- 
1 ered or sundered by 
crevasses, it re- 
unites and forms 
one compact mass. The crevasses admit warm air, and their walls 
are perhaps slightly thawed, or the ice on the top of the glacier 
being melted, water 
trickles down and 
moistens the fractured 
surfaces. In this con- 
dition the mass of 
fragments is com- 
pressed by its con- 
fining valley walls, the 
sundered portions are 
brought together 
again, and regelation 
occurs. 

Under pressure ice melts 
at a lower temperature than 
32° F. If a wire weighted at 
each end is caused to cut 
through a block of ice, 
water will be seen flowing 
round the wire, while, in 
the cut behind or above 
the wire, it is found to be 

frozen. This experiment has an impoftant bearing upon the phenomena of 
glacier motion. Pressure is obviously exerted by certain portions of the 




A Crevasse 
This fissure was encountered in making an ascent of the 
Jungfrau, Switzerland. From stereograph. Used by 
permission. 



MORAINES 



267 



glacier upon others, especially when the glacier is squeezed within gorges. 
If this pressure develop heat enough to bring the melting point of ice to 
28° instead of 32°, it is easy to see how the onward movement of the glacier 
would be facilitated by reason of its partial liquefaction. 

Moraines. — The rocks and 
debris brought down from the 
slopes of the ravine by the 
action of the frost and by 
avalanches accumulate 'on the 
sides of the glacier, forming 
dark bands of earth and 
stones, varying in size ac- 
cording to the character of 
the rock encountered. These 
bands are called moraines. 
Occurring at the sides they 
are called lateral moraines. 

At the confluence of two 
glaciers, the moraines which 
skirt the two sides that join 
are united, and form a medial 
moraine. If another glacier 
unites with this again, a 
second medial moraine is 
formed in the same man- 
ner. 

The earth, stone, and bowl- 
ders brought down on the 
glaciers form, at the lower 
end of the glacier, where the 
ice melts and leaves them, 
immense deposits called ter- 
minal moraines. 

Bowlders of Transportation. 
the surface is strewn with bowlders derived from distant sources. 
They evidently once formed a part of an old moraine, and their 




Moraines {a, b, c, d, e) of the Mer de 
Glace 



In 



the above cut it will be seen that 
the Glacier du Geant unites first with the 
Glacier des Periades, and from their junc- 
tion the dotted line shows the medial 
moraine formed from the right moraine of 
the Geant glacier and the left moraine of 
the Periades. Where the glacier thus re- 
inforced receives the Glacier de Lechaud, 
another medial moraine is formed; and a 
third where the Talefre adds its tributary 
stream. By the junction of these is formed 
the Mer de Glace. 

In some regions of the earth 



268 



HAIL, SNOW, AND GLACIERS 



presence is explained by the transporting power of glaciers. 
As the ice melted they were deposited in their present positions 
and sometimes so gently as to form the so-called rocking stones 
that may be swayed back and forth if pushed by the hand. 
These transported bowlders vary greatly in size. They may 
weigh hundreds of tons, but usually they diminish in size as the 






A Transported Glacial Bowlder, Yellowstone National Park 
This massive bowlder of granite is 24 feet long, 20 feet wide, and 18 feet high. To have 
reached its present position, near Inspiration Point, it must have been carried from 
30 to 40 miles. 

distance from their origin increases. A belt of country extend- 
ing from the Baltic to the Black Sea is strewn with bowlders 
rent from the Scandinavian mountains. 

The Glacial Period. — The former existence of extensive ice 
sheets over the northern portions of Europe and North America 
is evident. Among the proofs may be cited the following : the 
occurrence of smooth and polished rock surfaces ; striations and 



DRUMLINS, ESKERS, AND KAMES 



269 



grooves similar to those found in regions known to have been 
glaciated ; old moraines ; transported soils and bowlders ; valleys 
filled with transported rock waste ; ice-eroded rock basins now 
forming lakes. 

The time of this ice invasion in the earth's history dates from 
an age just preceding the probable advent of man. So exten- 
sive were the altera- 
tions of surface fea- 
tures then produced 
that sufficient time has 
not yet elapsed to ob- 
literate the evidence. 

Drumlins, Eskers, 
and Karnes. — In cer- 
tain glaciated areas, as 
in central New York, 
central and eastern 
Massachusetts, and 
southern Wisconsin, 
there are found hills 
and ridges of glacial 
debris or //// having 
an oval or elongated 
oval form and smooth, 
rounded surfaces. 
Their longer axes lie 
in the direction of the 
ice movement, as will 
appear from an ex- 
amination of the striae and grooves on the neighboring rocks- 
Such elevations have been termed drmnlins. Their height varies, 
but rarely exceeds 100 to 200 feet; their length also varies, 
ranging from a half a mile in the short forms up to a mile or 
even two miles in the more elongated forms. These hills are 
of a morainic character and often constitute the most prominent 
features of a landscape. 




Map showing the Area of North America 

covered by ice in the glacial period 

Salisbury. Geological Survey of New Jersey. 



270 



HAIL, SNOW, AND GLACIERS 




Glacial Grooves at Kingston, Iowa — Iowa Geological Survey 
In these groovings the movement of the ice body in four directions is recorded. 

Another topographic feature of glacial origin is seen in the 
winding or sinuous deposits of washed sand and gravel which 




Drumlin, Savannah, Wayne County, New York 
The right-hand end has been notched by the wave cutting of Lake Iroquois, the predeces- 
sor of Lake Ontario. From photograph by Professor H. L. Fairchild. 



GLACIERS AS RIVER SOURCES 2/1 

form well-defined ridges, rarely exceeding 50 feet in height and 
usually of less elevation. They are known as cskers. Their 
origin is somewhat obscure, but it is thought that they represent 
deposits of debris in subglacial streams flowing in tunnels or 
deposits in canyonlike gorges cut in the ice by stream wear 
and melting. 

Closely related to drumlins and eskers are mounds or knolls 
of sand and gravel, glacial debris, which has been more or 
less stratified through water action. These deposits have been 
termed kamcs. The materials of which they are composed 
were evidently deposited adjoining the ice by streams issuing 





Side View of Esker, Pittsford, x\e\v York 
From photograph by Professor H. L. Fairchild. 

from glaciers and, whenever the ice melted, left in the form of 
mounds. 

Glaciers as River Sources. — The glacier, as it imperceptibly 
glides down the moimtain, is melting all the time, and the 
traveler upon its rugged surface may hear, far down in its 
creviced depths, the sound of running water, which gathers 
volume from a thousand trickling streamlets, and at last issues 
forth, the never failing source of some noble river. 

The Rhine, the Rhone, and many tributaries of the Danube 
and Po spring from glaciers in the region around the Saint 



2/2 



HAIL, SNOW, AND GLACIERS 



Gothard ; and every one of the hundreds of glaciers found 
among the Alps nourishes some stream. The Ganges, in 
India, leaps out from under a glacier, a torrent 40 yards in 
width. 

Distribution and Size of Glaciers. — Glaciers of enormous size 
are found in the Arctic and Antarctic regions. In the Old 
World the grandest glacier region of the Temperate Zone is 
that of the Himalayas. The glacier of Bepho, in one of the 




A Group of Kames, Mendon Ponds, Monroe County, New York 
From photograph by Professor H. L. Fairchild. 



valleys of the Karakoram range, is 36 miles in length — about 
four times as long as the Mer de Glace — and covers hundreds 
of square miles in area. Many others in the same region are 
of nearly equal extent. 

It is estimated that the number of large glaciers in the Alps 
is about 500, and that the surface constantly covered by snow, 
neve, and ice is more than 1000 square miles. The thickness 
of the Alpine glaciers is believed to vary from 200 to 800 feet. 



ICEBERGS 



273 



The Pyrenees and the Scandinavian mountains contain glaciers, 
and large ones exist in the Caucasus. 

In the New World, Greenland and Alaska have glaciers far 
surpassing in magnitude those of the Old World. The Hum- 
boldt Glacier, in Greenland, is more than 60 miles in breadth and 
300 feet deep. The Malaspina Glacier of Alaska, according to 
Russell, has an area approximating 1500 square miles. He 
has described it as " a vast, nearly horizontal plateau of ice." 




An Iceberg 

Glaciers are also found upon Mount Shasta, upon Mount 
Rainier, and in the Selkirk Range in Canada. The Andes, 
except in Patagonia, are destitute of them. 

As distinguished from valley glaciers, continental glaciers or 
ice sheets cover the entire surface over large areas. They are 
great snow and ice plains or, if sufficiently elevated, plateaus. 
At present they occur in Greenland and the Antarctic regions. 
The ice sheets of the Glacial Period were undoubtedly of this 
type. 

Icebergs. — The glaciers of the polar regions are not melted 
into rivers like those of temperate latitudes. Their lower ex- 



274 HAIL, SNOW, AND GLACIERS 

tremity, therefore, is pushed out into the sea, and masses, often 
of great size, are broken off from time to time by the buoyancy 
of the water and borne away by ocean currents. These are 
called icebergs. 

On the polar side of 55°, soutli, the sea, all the way round the earth, is 
studded more or less thickly with icebergs. 

During his Antarctic voyage in 1841, Sir James Ross sailed 450 miles along 
an unbroken barrier of ice. It stood 180 feet out of the water, and was 
aground in water 1500 feet deep. 

Admiral D'Urville fell in with an ice mass off the Cape of Good Hope 13 
miles long and 100 feet high. Maury met with them as near the equator as 
37° south latitude. Indeed, icebergs come from the unexplored Antarctic 
regions in sufficient number to stud an area as large as the continent of Asia; 
for navigation is endangered there by ice throughout an area of not less than 
15,000,000 square miles. 

On the north side of the equator icebergs are found only in the Atlantic ; 
never in the Pacific Ocean. They drift out from their nurseries in the polar 
regions with the cold currents, which bear them southwardly until they dis- 
appear in the warm waters of the Gulf Stream. They frequently lodge on 
the Banks of Newfoundland, where they greatly imperil navigation. 



XXV. ELECTRICAL AND OPTICAL PHENOMENA 

Atmospheric Electricity. — Concerning the precise nature of 
electricity we are ignorant. Althougii known only by its mani- 
festations or effects, it has been defined as a "powerful physical 
agent." Among the phenomena attributed to it are shocks 
more or less violent, heating and 'luminosity, chemical action, 
attraction and repulsion, etc. Electricity is of two kinds, posi- 
tive and negative. The former is that developed on a glass rod 
by rubbing it with a silk cloth ; the latter that developed on a stick 
of seahng wax by rubbing it with a flannel cloth. Bodies charged 
with like electricity repel, while bodies charged with unlike elec- 
tricity attract each other. By the use of suitable instruments it 
has been shown that ordinarily the atmosphere is charged posi- 
tively and that the presence of electricity is by no means confined 
to showery weather or thunder storms. During.cloudy weather it 
may be either positive or negative, but during thunder or snow 
storms it may change from one to the other with great rapidity. 

The electric discharge known as lightning is a visible mani- 
festation of atmospheric electricity. It may occur between a 
charged cloud and the earth or between two oppositely charged 
clouds. It would seem that the cloud units or vapor particles 
are individually electrified and that upon condensation into 
drops the amount of electricity equivalent to that spread over 
the surfaces of the component vapor particles is, in the case of 
each drop formed, spread over a surface of much less area. 
From this it follows that each drop becomes more highly 
charged than its component units or is at a \\\g\\Qx potential. 

A cloud is formed of a vast number of water drops. As they 
further unite by condensation the potential of the cloud becomes 
still greater ; that is, the amount of electricity for a given sur- 
face area is increased more and more. If, under such condi- 

•275 



276 



ELECTRICAL AND OPTICAL PHENOMENA 



tions, the cloud should approach the earth, a disruptive dis- 
charge through the intervening air may take place or the same 
phenomenon may occur upon the approach of two oppositely 
charged clouds. 

Lightning flashes are of several kinds — stream lightning, zig- 
zag lightning, sheet lightning, and ball lightning. 
Stream lightning consists of a broad, straight flash. 
Zigzag lightning consists of flashes passing between two 
bodies of air or clouds, or between a cloud and the earth. Since 

different portions of 
the air have different 
conducting powers, 
and the electricity fol- 
lows the path of least 
resistance, the course 
of the lightning natu- 
rally becomes zigzag. 
Sometimes the flash is 
forked. 

Sheet lightning, fre- 
quently called heat 
lightning, appears as 
a glow of hght illumi- 
nating vast clouds and 

ZIGZAG LIGHTNING. FROM A PHOTOGRAPH ^^^^^ J^^^^ ^^^^^ ^f 

the sky. It is probable that this kind of Ughtning is the reflec- 
tion of the lightning of some distant storm. 

Ball lightning appears in the shape of globular masses of fire, 
which explode with violence. It is of rare occurrence. 

Thunder is considered to be occasioned by the sudden rushing together of 
the portions of the atmosphere that have been divided by a flash of lightning. 
It is not often heard at a greater distance than fourteen miles. Occasionally, 
however, in level regions such as the prairies, it may be heard at a very much 
greater distance. 

The flash is seen instantaneously, because light travels about 186,000 miles 
in a second. The sound requires about five seconds to travel one mile. 
Hence if, after seeing the lightning, we count the number of seconds, or pulse 




THE AURORA 277 

beats, until we hear the thunder, it is easy to ascertain how near the flash has 
been to us. 

In general the electricity does not pass from the air to the 
earth, but only from one portion of the atmosphere to another. 
When a discharge to the earth does occur, the effects are often 
very destructive. The strongest trees, if struck, are rent and 
stripped of their branches, the sap being suddenly converted 
into steam, and an explosion actually taking place. Animals 
and men who are struck are almost always killed. 

The Aurora. — Another phenomenon, in which atmospheric 
electricity apparently plays an important part, is the illumina- 
tion, often a magnificent display of color, frequently seen near 
the polar regions of the earth. It takes on a variety of forms. 
Sometimes it is simply an arch of Hght spanning the sky from 
east to west near the horizon, with quivering streamers of white, 
green, or crimson light, shooting fitfully to the zenith. Some- 
times mere masses of colored light are observed. Again the 
whole heavens are flushed. 

In the northern hemisphere it is called the aurora borealis 
(" Northern Lights ") ; in the southern hemisphere, the ainvra 
anstralis (" Southern Lights "). Of the two displays the former 
is better known. The zone of its greatest brilliancy is slightly 
irregular, lying, for the most part, between the parallels of 60° 
and 70° north latitude. It follows roughly the Arctic shore 
line of the Eastern Hemisphere, but in the Western Hemisphere 
it passes southeast from Alaska to Hudson Bay, thence south of 
Greenland and Iceland to the northern shores of Scandinavia. 

Auroras are more frequent as we approach the poles. Within 
the tropics they are almost unknown. Their law of distribution 
seems to be the reverse of that which governs the distribution 
of lightning. 

The following facts show that the aurora is an electrical 
phenomenon: — 

(i) The delicate shades of rose, purple, and violet, which characterize the 
more brilliant auroras, can be produced experimentally by passing currents of 
electricity through vacua in Geissler tubes or receivers. 



2/8 



ELECTRICAL AND OPTICAL PHENOMENA 






It has been computed, from observations of a large number of auroras, that 
the beams do not usually approach nearer to the earth's surface than 50 miles, 
and sometimes extend from it to the distance of more than 250. At such 
altitudes the atmosphere must necessarily be very attenuated, like that through 
which the electricity is passed in the experiments alluded to. 

(2) Direct evidence of the electric character of the aurora is found in the 
eifect produced upon telegraph wires during an auroral display. The aurora 
has sometimes caused the instruments to work, as though it had been a battery. 
Sometimes it completely interrupts their work. 

(3) The magnetic needle, also, is frequently disturbed during auroras in a 
degree corresponding to their brilliancy. 

Saint Elmo's Fire. — In storms at sea the masts and yards 
of the ship are sometimes tipped with balls of electric light. 

They are due to elec- 
tricity passing without 
noise, when the clouds 
are low, between the 
clouds and the tips of 
the spars of the ship. 
Optical Phenomena. 
— The most impor- 
tant of all the optical 
phenomena connected 
with the atmosphere 
is also the most com- 
mon. It is the diffu- 
sion of light. This is 
brought about by reflection and refraction. By the former, 
light is propagated from particle to particle in the atmosphere. 
By the latter, it is retained above the horizon when the sun has 
actually gone down, and it is bent into the atmosphere before 
he has actually risen above the horizon. 

Refraction and reflection give rise to the exquisite variety of 
colors which deck the morning and evening sky. They also 
occasion the phenomena of rainbows, parhelia (commonly called 
sundogs or mock suns), paraselense (or moondogs), halos, and 
mirage. 



m 









OPTICAL PHENOMENA 2/9 

The rainbow is an arch of colored Hght which spans the heavens during a 
storm. It is seen only when the sun is shining at the same time that rain 
is falling. The descending drops separate the white sunlight into its ele- 
mentary colors. 

Halos are rings of prismatic colors round the sun or moon. They are really 
circular rainbows, probably due to the refracting power of the ice crystals com- 
posing cirrus clouds. 

Mirage. Another effect of refraction and reflection is commonly called 
fftirage. It is often observed in the desert. Distant villages seem under its in- 
fluence to be near to the spectator or to be suspended in the heavens above. 
Sometimes the traveler thinks he is approaching a pool of sparkling water, and 
hastens to quench his thirst, when he finds that he has been pursuing a mirage. 
Mirage is also observed at sea, distant ships being seen elevated above their 
true po.sition, or even inverted in the air. 



M.-S. PHYS. GEOG. — 1 7 



PART v. — LIFE 

XXVI. ANIMALS AND PLANTS: THEIR 
RELATIONS AND DISTRIBUTION 

Inorganic and Organic Bodies. — In the preceding chapters at- 
tention has been especially directed to the land, the water, and 
the air. They constitute the inorganic or lifeless portions of the 
earth. The following pages treat of living bodies, including Man 
himself. As such bodies are possessed of parts adapted to certain 
ends, — for example, lungs for breathing, feet for walking, eyes for 
seeing, — they are said to possess organs having certain func- 
tions, hence all such bodies are organic. It is customary, there- 
fore, to speak of mineral matter as inorganic and of living matter, 
or that formed through the process of living, as ofganic. 

Of living things two grand divisions are recognized : plants 
and animals. In the study of Physical Geography it is necessary 
to consider, first, the relations of each of these divisions to the 
other ; and secondly, their distribution and its causes. 

Animals and Plants. — In their higher forms animals and 
plants are easily recognized, but lower in the scale of life the 
distinguishing characters of each become less marked until 
eventually forms are encountered which are recognized as ani- 
mals or plants with the greatest difficulty and at times with much 
uncertainty. 

The higher animals differ from the higher plants in many 
particulars, among which mention may be made of the following : 
They have a nervous system ; they are not fixed in position, but 
possess the power of voluntary motion ; they have an internal 
cavity adapted to the digestion of solid food. The higher plants, 
on the other hand, are without a nervous system ; they are fixed 

280 



ANIMALS AND PLANTS 



281 



in position, that is, they are without the power of voluntary 
motion ; and their nourishment, unUke that of animals, being 
liquid or gaseous, does not require a digestive cavity. In con- 
sequence of these distinctions common animals and plants are 



.-f-'*'S^,- 




VlCTORIA REGIA 

rarely confused. When, however, the lower forms of animals 
are reached, especially those which are attached or fixed to for- 
eign objects during the whole or a part of their lives, then there is 
great danger of mistaking them for plants. The sea anemone 
and the coral polyp, for instance, are both plantlike in appear- 
ance, the spreading tentacles about their mouths presenting a 
flowerlike fringe. 



282 ANIMALS AND PLANTS 

Plants, in general, differ from animals in their power of trans- 
forming inorganic matter into living matter. Animals do not 
possess that power. Hence for their food animals are dependent, 
either directly or indirectly, upon plants. Animals feeding upon 
plants are herbivorous ; those feeding upon other animals are 
carnivorous. Where there is neither grass nor other vegetable 
growth, herbivorous animals cannot live ; and where they are 
not found, carnivorous animals, which feed upon them, cannot 
exist for want of a food supply. 

General Facts concerning Distribution. — It is a familiar fact 
that the same kinds of plants and animals are not found every- 
where. Some forms are widely distributed, others are restricted 
to very narrow limits. The region within which any plant or 
animal is found is commonly called its geographical range. The 
dandelion and buttercup blossom even amid the glaciers of 
Greenland. The orange, the date, and banana grow only within 
or near the tropics. The gigantic water lily called the Victoria 
Regia has been found only in the basins of the Amazon and 
Orinoco. 

Range Dependent on Climate. — Certain conditions render it 
possible or impossible for the various species of living forms to 
exist. Of these conditions by far the most important are tem- 
perature and moisture. 

The peculiar plants and animals of the torrid zone would ob- 
viously die, if placed amid the cold of the Arctic circle ; while 
it is equally certain that the polar bear and his associates would 
become extinct, if they were exposed to the scorching heat of 
the tropics. 

The early geological history of the globe furnishes striking illustrations of 
this principle. The entire assemblage of animals that we now find upon the 
earth did not simultaneously spring into existence. Those species first ap- 
peared which were suited by existing climatic conditions. Low forms of ani- 
mal life prevailed at first, and then higher and higher successively, until such 
conditions arose as were favorable to the life of Man, and then, at length, his 
creation took place. 

Many, moreover, of the animals that once abounded have entirely disap- 
peared. Their existence is attested only by fossil remains. Lynxes, bears, 



MODIFICATIONS BY CLIMATE 283 

and hyenas once roamed over the fields of England, and crocodiles swarmed 
in its rivers ; huge mastodons, larger than the modern elephant, flourished on 
what are now the banks of the Hudson, and browsed amid the forests of Si- 
beria. Their tusks are dug up at the mouth of the Lena and upon the islands 
of New Siberia, in such quantities as to form an article of regular commerce, 
under the name " fossil ivory." The climatic conditions favorable to their 
existence have ceased, and their race has therefore become extinct. 

Modifications by Climate. — It would follow as a natural con- 
clusion from the fact that plant and animal life are largely de- 
pendent on physical conditions, that changes in these conditions 
should bring about changes in the' plants and animals affected 
by them. Such we find to be the fact. Modifications of a very 
extraordinary nature can be affected by varying the " environ- 
ment" of a plant or animal, and allowing the new environment 
to be permanent during a sufficient length of time. Many of 
our most valuable food plants have been thus transformed. The 
grains in general are believed to have been originally wild 
grasses. 

Our own Indian corn presents a very interesting illustration of 
climatic modification in a vegetable form. In the South and the 
Northwest it often attains the height of 12 to 15 feet. As we 
advance northward through its belt of cultivation, along the At- 
lantic slope, its height diminishes, until, in New England, it is 
not usually more than about five feet high. Again, the appearance 
and quality of its grain have been singularly modified. It is a 
familiar fact that we have a number of varieties, field corn, sweet 
corn, pop corn, with white, yellow, brown, and even black grains. 

Similar illustrations might be given of the modifications of 
animal forfns by changes in their physical conditions. The 
Shetland pony and the race horse came from one original stock. 
The terrier, the greyhound, and the mastiff had a common 
parentage. 

Zones of Vegetation. — Since the extent of the geographical 
range of plants depends mainly on temperature and moisture, it 
follows that the surface of the earth may be divided into zones of 
vegetation. These will correspond more or less closely with the 



284 ANIMALS AND PLANTS 

zones of temperature. They will of course be defined not by lines 
of latitude, but by lines of heat, or isotherms. 

The principle of division is this, that within belts or zones 
having a certain average annual temperature, certain plant 
growths will flourish ; beyond the limits of such zones these 
characteristic forms disappear, and others are found which are 
suited to the prevailing temperature. Thus each zone has its 
characteristic forms of plant life. 

Although in naming the zones of vegetation the same terms 
are employed as in the ordinary divisions by lines of latitiide, it 
should be borne in mind that the signification of the terms has 
been slightly changed in order to accord with lines of tempera- 
tiLve. 

Horizontal Zones. — - The surface of the earth may be divided 
into the following horizontal zones of vegetation: (i) an equa- 
torial zone ; (2) two temperate zones ; (3) two polar zones. 

The Equatorial Zone extends north and south of the equator, 
and is bounded by the annual isotherms of 70°. It is the zone 
of greatest heat and most abundant moisture, and consequently 
of most luxuriant vegetation. 

The characteristic growth of this belt is that of the palms. 
The trees do not lose their leaves in winter. 

The Temperate Zones extend northward and southward of 
the equatorial, and are bounded by the isotherms of 32°F. Here 
the tropical palms disappear, or are replaced by dwarfed repre- 
sentatives of the family. 

The characteristic forms are those of the deciduous forest 
trees, — those which shed their leaves in autumn and renew 
them again in spring, — of which the oak, the chestnut, and 
others belonging to our own forests are familiar examples. 

The colder parts of these zones are marked by the abundance 
of conifers (pines, larches and spruce, and juniper trees). 

The Polar Zones extend north and south from the temperate. 
Within them the average annual temperature is not higher than 
32°F., and in many portions it is below 5°. The warmer parts of 
these zones contain vast forests of spruce, pine, and larch. The 



HORIZONTAL ZONES 



285 




A Group of Date Palms 
A scene in the town of Luxor on the Nile. 



colder portions are characterized by the growth of dwarfed 
birch, alder, and willow trees. But beyond certain limits trees 



286 



ANIMALS AND PLANTS 




wholly disappear, and only the lowest forms of plant life 
(mosses and lichens) remain. 

Vertical Zones. — Since, by ascending sufficiently high, even 
in equatorial regions, one can pass through every variety of 
climate, torrid, temperate, and frigid, it is clear that there 
must be vertical as well as horizontal zones of vegetation. 

On the lower slope of the Andes, for example, are found 
regions of palms and bananas, tree ferns and vines. These 
correspond to the zone of equatorial vegetation. Higher up are 
encountered the deciduous trees of the temperate zone. Still 

farther up 

there is a re- 

#/ ] j|/^'-V gion closely re- 

.i&S^^\ Region of Lichens. SCmbling the 

I ^-^ ^^^^-S. ^I^ i ;^A^ Shrubby Region. Conifers are 

£ '""7S3!iH!M^Wv'^^^^^ the prevailing 

3. f9>0 '^^■^^ Si-p 9 5^ ^*'°" °^ ordinary large trees, type, whilc dc- 

i y^\\f i^lt'Ih'' [ I ^i '"!> O^Kegions of the Vine. ciduOUS trCCS 

a 'J^^'J'^^y?iy^^^^^ ^^^ represent- 

y^"-^--^'^'^":r^0Sd^M^i^^^^ KegionofPaims. cd by shrubs 

^ ^-^^ '' '^^'^^^^ri'.' ^.^^^,.. and dwarfed 

Vertical Zones of Vegetation „ ,• »., ^ ^ 

specimens. 

Near the snow line trees of every kind disappear, and mosses 
and lichens are the only forms of vegetation that can with- 
stand the perpetual cold. 

The Flora of the Sea. — The flora of the sea differs from that 
of the land in color. It is less inclined to green. The plants 
of the sea are brown and yellow, pink and purple, green, 
orange, and violet, with all intermediate shades. 

The vegetation of the sea has, hke that of the land, a vertical 
and a horizontal distribution. Both are determined mainly by 
the temperature of the water and the nature of the sea bed. 

In the deepest parts of the ocean nothing but microscopic 
forms of vegetable life of the simplest kind (called diatoms) 
occur. The smaller algas or seaweeds scarcely exist below the 



THE FLORA OF THE SEA 28/ 

depth of 300 feet ; the larger are not found deeper than about 
60 feet below the surface. The horizontal range of many 
marine plants is coextensive with the sea. Others, like land 
plants, have hmited ranges. 

Among the most interesting kinds of algae are the Macrocystis 
pyrifeTa, the U UrvillcEa ittilis, and the Gulf Weed. 

The Macrocystis pyrifera measures 700 feet in length. This weed is like 
a cord. It attaches itself to the rocks, and grows from the bottom in the 
littoral waters of many countries, and especially along the northwest coast of 
America. 

Few, if any, forms of vegetation have a wider geographical range than this 
weed. After all traces of plant life on the land have ceased, on approaching 
the poles, it is still found flourishing in the water. 

The D^ Urvillcea iitilis grows in the waters of the Falkland Islands and ad- 
joining regions. The surf often twists it into cables several hundred feet long 
and as thick as the human body. This, like the Macrocystis pyrifera^ fastens 
itself to the rocks, in stormy waters, with such tenacity that sometimes, 
in the attempt to tear it away, large bowlders are brought up adhering to its 
roots. It is used as food in Chile. 

Plants of this species surround Kerguelen Land with such a tangled mass 
that rowboats find it difficult to get through it. The Straits of Magellan are 
so thick with these weeds that they fouled the rudder and so entangled the 
propellers of the first steam vessels that passed through these waters as 
seriously to interfere with the navigation. 

Among the most widely distributed forms of marine vegetation is the Gulf 
Weed (^Fuciis natans'). It is not known whether it grows at the bottom or 
near the surface of the sea. It is always found afloat, living and growing, but 
without any signs of roots. It lies so thick in the Sargasso Sea as completely 
to hide the waters in many places and give the sea the appearance of a drowned 
meadow. 



XXVII. THE DISTRIBUTION OF USEFUL PLANTS 

Food Plants. — It will be of interest to consider the geo- 
graphical distribution of those plants that are of the greatest 
importance to man. Of these, the grains or cereals, as they 
are called (barley, rye, wheat, Indian corn, rice, and millet), 
deserve first attention. Certain of them have, of all plants, the 
widest geographical range. 

Barley is cultivated in Europe as high as 70° north latitude, 
and on the Asiatic table-lands at an elevation of 13,000 feet. 

Rye will grow in all regions between 6']° north and south 
latitude. 

Wheat has a range almost equal to that of rye. It ripens in 
North America as far as latitude 55°, and in Europe, owing to 
the influence of tempering winds and currents, as far as latitude 
64°. In Mexico and the Andean region its culture begins at 
the height of about 2500 feet and is successful as high as 
10,000. Upon the Himalayas it is cultivated as high as 12,000 
feet above the sea. 

Indian corn will grow and ripen in the open air, from the 
parallel of 45° or 50° north to the corresponding parallel south. 
Its range embraces two thirds of the earth's surface. In the 
torrid zone neither wheat nor Indian corn do well at the sea 
level, though they produce finely on the mountain sides. 

Rice is limited in its geographical range by the parallels of 
45° north and 35° south. This belt covers more than half the 
surface of the earth. The plant thrives best in low and 
swampy ground, and is the chief cereal cultivated in China and 
Japan. Its grain is the principal article of food for one third 
of the entire human race. 

Millet is the most prolific of the cereals. It is adapted better 
than any other to the vicissitudes of a tropical climate. In 

288 



FOOD PLANTS 289 

Egypt, Arabia, Turkey, and Italy it is an important article of 
food, and in India it, and not rice, is the staple food grain. 

Nearly allied to the cereals as an article of diet is the potato. 
It has a range almost equal to that of barley. It is probably a 
native of Chile or Peru, but will grow in Iceland. 

In the low, damp, and hot portions of the equatorial region, 




Breadfruit 

wheat and corn are replaced by rice and the banana, mandioca, 
and the breadfruit. 

The banana, indigenous in the regions of intertropical Amer- 
ica, is, as an article of food for the masses, what rice is to the 
Hindu, the potato to the Irish, and wheat to the European. 
An acre of ground planted in bananas requires less cultivation 
and yields more abundantly than any other food plant. Hum- 
boldt estimated the yield to exceed that of the potato 44 times, 



290 



THE DISTRIBUTION OF USEFUL PLANTS 



and that of wheat 133 times. The banana flourishes 4000 feet 
above the sea. 

Mandioca or cassava is a native of South America. It is also extensively 
grown in Africa and other tropical regions. Its large turniplike root, dried 
and grated, is the food of a large part of the population of South America. 

Breadfruit is characteristic of the islands of the Pacific. Its fruit, repre- 
sented in the cut, furnishes the natives with food somewhat resembling bread. 

Sugar cane, so far as we know its history, seems to have been a native of 
India or China. It grows in the warm latitudes of every continent. 

Beverage Plants. — The chief plants which yield beverages, tea, 

coffee, and cacao, are 
grown in warm re- 
gions ; tea in China 
and Japan, India, 
and Ceylon ; coffee 
in southern Asia, 
central Africa, and 
the tropical portions 
of North and South 
America. Cacao is 
a native of the trop- 
ical regions of North 
and South America. 
Spices and Narcot- 
ics. — The geograph- 
ical range of the 
spices, such as cin- 
namon, nutmeg, gin- 
ger, pepper, cloves, 
allspice, and pimen- 
to, is narrow. It is 
confined to a few 
degrees north and 
The East, Indies are specially the region 




Nutmeg 



south of the equator 
of the spices. 

The important narcotics, tobacco and opium, are natives of 



PLANTS USED FOR CLOTHING .291 

warm regions, but their geographical range extends into the 
temperate zones. 

Plants used for Clothing. — The principal plants which are 
used for textile fabrics and clothing are cotton, flax, and hemp. 

Cotton, the most important of them all, will grow and mature 
well at moderate heights, anywhere between the parallels of 
37^° north and south. This belt being 75° of latitude broad, 
and extending entirely round the earth where its circumference 
is largest, gives for this plant a geographical range that em- 
braces more than half the earth's surface. 

The United States, Brazil, India, and Egypt are the chief 
cotton-growing countries. 

Flax and hemp are confined to the climates of the temperate 
zone, and are brought to their greatest perfection between the 
parallels of 25° and 50° north. 

The Medicinal Plants, such as yield sarsaparilla, jalap, castor 
oil, quinine, gums, and balsams, are almost all indigenous to 
the torrid zone. 

Foremost among them stands the cinchona, from which 
quinine is obtained. Is is a native of the eastern slopes of the 
Andes, flourishing in a belt that extends through Bolivia, Peru, 
and Equador, from 3000 to 9000 feet above the sea level. It 
has been successfully acclimatized in India. 

Useful Trees. — The ornamental woods and dyewoods, such 
as m.ahogany, rosewood, sandalwood, and logwood, are confined 
to the torrid zone. The oak, walnut, chestnut, maple, ash, with 
pines, firs, and cedars, belong to the cooler latitudes. 

The geographical range of the oak extends from the tropics 
to the verge of the frigid zone. The timber trees of the tem- 
perate zone are replaced in the torrid by the teak and bamboo. 



XXVIII. THE DISTRIBUTION OF ANIMALS 

General Statements. — -Animals, like plants, require a certain 
temperature for the maintenance of their life. Furthermore, 
no animal except Man can inhabit regions in which nature does 
not spontaneously provide for it suitable food ; and hence the 
fauna of every country is dependent on its flora. For these two 
reasons the distribution of animals, like that of plants, depends 
mainly upon climate. 

Zones of Animal Life. — In view of this fact it is usual to 
divide the earth's surface, in relation to its fauna, into the equa- 
torial, temperate, and polar zones, as has been done in treating 
of the distribution of plants. 

The Equatorial Zone is characterized by the abundance of its 
forms of animal life. It is the zone of lions, tigers, rhinoceroses, 
elephants, camels, crocodiles, poisonous serpents, and birds of 
the most brilliant plumage. 

The temperate zones, on the other hand, are distinguished by 
the number of their useful animals, such as the ox, cow, horse, 
sheep, and goat. The eagle, turkey, and pheasant are among 
the birds. In coloring, the animals of temperate regions are far 
less brilliant than those of the Equatorial Zone. 

In the Arctic regions (for of the Antarctic we know little) are 
found the fewest species, although the individuals are numerous. 
The reindeer, musk ox, white and brown bear, wolves, white 
foxes, and sables are the chief land animals. The seal, walrus, 
and whale frequent the waters. Reptiles are unknown. Ducks 
and gulls abound. 

Zoological Regions. — It is obvious that any division of the 
earth's surface into zones characterized by peculiar fauna and 
flora is necessarily far from exact. Although the distribution 

292 



ZOOLOGICAL REGIOxNTS 



293 



of life on the globe is mainly dependent on climate, it is not so 
altogether. 

For, in the first place, many species overlap, being found in 
more than one zone. 
The dog is the com- 
panion of Man in 
every zone ; sugar 
cane grows in both 
torrid and temperate 
regions. 

And in the second 
place, however alike 
in climate different 
portions of the 
earth's surface may 
be, they do not nec- 
essarily have the 
same flora and fauna. 
The isotherms of 
the United States 
traverse also the 
Empire of China. 
Yet there are marked 
differences between 
the forms of plant 
and animal life which 
characterize the two 
regions. The iso- 
therms of 68° F. pass 
through Australia, 
South America, 
China, and the Gulf region of the United States. But the vege- 
tation and animal life of these regions are strikingly diverse. 

From these considerations scientific men have been led to seek 
a mode of division more in harmony with existing facts than that 
represented by zones, and the plan proposed by the eminent 




Chimpanzee 

From photograph. Used by permission of the New 
York Zoological Society. 




DI 
THE PRIN 

The Colors 



Greenwich 30 



(294) 




30 Longitude 60 



from 120 Greenwich 150 



(295) 



296 



THE DISTRIBUTION OF ANIMALS 



naturalist Sclater, and more exactly defined by Mr. Wallace, 
seems to be the most satisfactory thus far devised. 

According to this division the surface of the earth is made 
up of six regions, each of vv^hich has certain forms of life 
peculiarly its own and not found elsewhere, although it may have 




Haki;.\k\ LH_)i\ 
From photograph. Used by permission of the New York Zoological Society. 

many species in common with other regions. The following 
are the names of the regions with their leading characteristic 
forms. 

(i) TJie NortJiern Old World Region includes all of Europe, 
all temperate Asia north of the Himalayas, and northern Africa 
down to the Tropic of Cancer. Here we find the bear, wolf, 
deer, horse, cow, and camel, the wild goats, the eagle, the corn- 
crake, and bustard. 

Peculiar to this region are almost all the known species of 
goats and sheep, moles and dormice ; and among birds the night- 
ingales, magpies, and almost the entire group of pheasants. 

(2) The Ethiopian or Africaji Region QTahrs-CQS Africa south of 
the Tropic of Cancer, southern Arabia, and the island of Madagas- 



ZOOLOGICAL REGIONS 



297 



car. Here we lose sight of certain forms familiar in the Northern 
Old World Region, bears, deer, moles, and true pigs ; and camels 
and goats, except in the desert regions, are equally wanting. 

Peculiar forms are the gorilla, chimpanzee, and baboon, the 
hippopotamus and giraffe, the guinea fowls, most of the weaver 
birds, and the secretary bird. 




HU'POPOTAMUS 

From photograph. Used by permission of the New York Zoological Society. 

Madagascar and the neighboring islands, though classed as parts of the 
Ethiopian region, have a fauna peculiar to themselves. This insular sub- 
region is one of the most wonderful in the world from a zoological point of 
view. It is especially characterized by the abundance of lemurs (nocturnal 
animals somewhat resembling monkeys, but very small) ; while most of the 
groups in which Africa is especially rich — apes, lions, leopards, giraffes, ante- 
lopes, and elephants — are wholly wanting. Some of the birds are entirely 
unlike all other known species. 

(3) The Indian Region comprises India, Indo-China, and the 
East Indian Islands as far as the Strait of Macassar. 

Peculiar to this region are the orang-outang, the tiger, the honey 
bear, the civet, and flying lemurs ; and among the bright-feathered 



298 



THE DISTRIBUTION OF ANIMALS 



birds, the argus pheasant, the peacock, the trogon, and the curi- 
ous little tailor birds. 

(4) TJie Australian Region consists of Australia, New Zealand, 
Polynesia, and those of the Malayan islands that lie east of the 
Strait of Macassar. 

This region has a fauna of marked peculiarity. It is notable 

for the absence of 
forms elsewhere al- 
most universal. The 
higher mammalia of 
other regions are re- 
placed by mammals 
(such as the duck 
mole) that lay eggs ; 
and by marsupials 
(that is, animals with 
a pouch for holding 
their young). Of 
these none are found 
elsewhere, except the 
opossum of North 
and South America. 
Among the marsu- 
pials of Australia are 
the kangaroo, the tree 
kangaroo, and the 
wombat. 

The bird life of 
this region is rich in 
handsome and pecuhar forms, such as the beautiful bird of 
paradise, the crimson lory, the lyre bird, the bower bird, the 
emu, and the cassowary. 

(5) The North American Region includes North America and 
adjacent islands north of the Tropic of Cancer. 

The fauna of this area and that of the Old World region 
present marked dissimilarities. Here we do not find native 




Three-horned Giraffe • 
Copyright, 1905, by New York Zoological Society. Used 
by permission. 



ZOOLOGICAL REGIONS 



299 



the horses, asses, cows, sheep, pigs, hedgehogs, and dormice 
of the Old World. They are replaced by the bison (nearly 
extinct), raccoons, opossums (marsupial), prairie dogs, and 




Orang-outang 
From photograph. Used by permission of the New York Zoological Society. 



skunks. The thrushes, wrens, robins, and finches are rep- 
resented by new families. 

Among animals peculiar to this region are the grizzly bear, 
the pouched rat, the mocking bird, the blue jay, the blue crow, 
and the rattlesnake. 

It is hardly necessary to say that many Old World forms 
have been introduced. 

(6) The South American Region embraces South America 
and that portion of North America and the outlying islands 
which are south of the Tropic of Cancer. 

Of all the regions this is the most remarkable for the fewness 
of the forms which it contains in common with others. No 

M,-S. PHYS. GEOG. — 1 8 



RANGE OF DRAUGHT ANIMALS 3OI 

horse or ass, ox, sheep, or goat is a native of South America. 
The wild cattle and horses which now roam over its plains and 
pampas are the offspring of animals introduced by Europeans. 

This region is equally remarkable as containing a greater 
number than any other of forms which are strictly its own. 
Among these are the sloth, the armadillo, the llama, the alpaca 




Great Gray Kangaroo 
From photograph. Used by permission of the New York Zoological Society. 

and chinchilla, the blood-sucking vampire bat, the prehensile- 
tailed monkey,^ and the destructive boa-constrictor. 

Here alone we find the condors, toucans, todies, rheas, curas- 
sows, and mot-mots. The forest-clad slopes of the Andes are 
alive with the murmur of 400 species of humming birds, some 
of which pass their existence near the limits of perpetual snow. 

Range of Draught Animals. — Of special interest is the geo- 
graphical range of those animals which Man employs as draught 
animals or beasts of burden. 

The horse, the ass, and the ox, either native or introduced, 
are found wherever grains and grasses grow. Beyond the 

^ Monkeys whose tails are capable of grasping the branches of trees. 



302 



THE DISTRIBUTION OF ANIMALS 



limits of these food plants the reindeer and the dog become 
the draught animals. The reindeer is fitted to browse upon 
Arctic mosses, and has the instinct of searching for them 




Silver-tip Grizzly Bear 
From photograph. Used by permission of the New York Zoological Society. 

beneath the snow. He presents one of the most striking 
cases of an animal adapted to the peculiar conditions of his 
habitat. 

In the equatorial regions of the Old World we find the ele- 
phant serving as a beast of burden ; while to the northward, 
especially in desert regions, the camel and dromedary are 
employed. 

The cushioned foot of the camel enables him to tread firmly upon the 
shifting sands of the desert^ while his capacity for carrying an extra supply 
of water adapts him wonderfully for journeying through its dry and thirsty 
wilds. 

In South America, where, to traverse the continent, the 
traveler has to scale the snowy heights of the Andes, there — 



RANGE OF DRAUGHT ANIMALS 



303 




South American Condor 
From photograph. Used by permission of the New York Zoological Society. 




The Camel as a Beast of Burden 



304 



THE DISTRIBUTION OF ANIMALS 



and not in North America, where the mountains have gaps 
that the buffalo could cross — was found the llama, the camel 
of the New World, the only beast of burden in use among the 
native Americans at the time of the discovery of the continent. 




Malay Tiger 
From photograph. Used by permission of the New York Zoological Society. 

The llama, with the alpaca and vicuna, which are different species of the 
same genus, have their habitat along the edge of the snow hne on the Andes, 
where the atmospheric pressure is not more than eight or ten, instead of 
fifteen, pounds to the square inch. 

This diminished pressure of the atmosphere has very marked effects upon 
both man and beast. To one from the lowlands, respiration, in these elevated 
regions, is difficult. Mules are used for the transportation of merchandise be- 
tween these places and the seaboard, but never ascend beyond a certain height. 
At the elevation of 5000 or 6000 feet- they are met by the llamas of the table- 
land, and the cargoes are exchanged. 

Without the camel and the llama Man, in the early stages of civilization, 
could have neither crossed the deserts of the Old World, nor scaled the cloud- 
capped mountains of the New. 

Among the fastnesses of the Hiinalayas, and upon the bleak heights of the 



LIMITED RANGE OF SOME ANIMALS 305 

Plateau of Tibet, the beautiiul yak serves as a beast of burden. He is to be 
seen browsing at an elevation of 17,000 feet above the sea. What the camel 
is to the Arab, what the llama is to the Peruvian, the yal<; is to the native of 
Tibet. 

Limited Range of Some Animals. — Many animals are con- 
fined to a very narrow geographical range by causes that are 




Two-TOED Sloth 
From photograph. Used by permission of the New York Zoological Society. 

in some cases quite obscure. The little chinchilla, with its 
beautiful fur, has its habitat on the Andes of Chile and Peru, 
8000 to 12,000 feet above the sea. 

The chamois inhabits the belt of the Alps which lies between 
the trees and the snow line. 

The Kashmir goat, noted for its fine wool, is restricted to 
the valleys of the Himalayas. 

The ostrich of Africa, the rhea of South America, the emu 
of Australia, the cassowary of Papua, the apteryx of New 
Zealand, are birds which neither fly nor swim. Their geo- 



306 THE DISTRIBUTION OF ANIMALS 

graphical range therefore is very limited. The same was true 
of the dodo of Mauritius and the sepyornis of Madagascar. 

Animals of limited range are the most likely to become ex- 
tinct. The apteryx is nearly so; the dodo has become so 




SoL'i'H American Llama 
From photograph. Used by permission of the New York Zoological Society. 

within two centuries ; and the aepyornis became so at a very 
recent period, for one of its eggs (eight times as large as that of 
an ostrich) was found and brought to Europe in 185 1, 

Fauna of the Sea. — As with the animals of the land, so with 
those of the sea — different species have their geographical 
range, both vertical and horizontal, beyond the limits of which 
the conditions necessary for their existence are not found. 
This, however, is less rigidly true with regard to the fauna 
of the sea than that of the land. It is quite obvious that 
temperature must be the main element which determines the 
habitat of marine animals. Other matters, such as the nature 
of the sea bottom, have a minor influence. 



3o8 



THE DISTRIBUTION OF ANIMALS 



Life of Tropical Waters. — The waters of the tropics, Hke the 
shores which they bathe, teem with the greatest variety of 
animal forms. Many of the fish and crustaceans are decked 
with colors of surprising brilliancy. 

The sperm whale inhabits the warm waters of this zone, 
and is most abundant in the Pacific Ocean. Flying fish, alba- 
core, bonito, and 
sharks are all in- 
habitants of inter- 
tropical seas. Pearl 
oysters, also, with 
corals and sponges, 
are found in this 
belt. 

Life of Cooler 
Waters. — In the 
cooler seas of the 
temperate and 
Arctic regions we 
find the greatest 
abundance of fish 
that are of value to 
Man. All the famous food fisheries in the world — those of 
the cod, the herring, the mackerel, and others — are in the 
waters of cold currents. 




After Yx 
From Nicholson and Lyddecker. 



The Grand Banks of Newfoundland, the fisheries of the North Sea, and 
those of the Pacific coasts of America, China, and Japan, all lie within the 
range of the cold flow from the north. It is to the presence of the cold 
current along our Atlantic seaboard that our own fish markets ov/e their 
celebrity. 

The right whale is found in the cold waters of polar seas. Those of the 
torrid zone are as impassable to him as a sea of flame. So true is this that 
the right whale of the northern hemisphere and the right whale of the south- 
ern are restricted each to his own zone. 

Although the seal may be found in all latitudes, his favorite haunts are 
the islands of Alaska, the shores of Labrador, and the bays of Patagonia. 
Other inhabitants of polar waters are the sea lion, hunted for his fur, and the 



THE FLORAS OF THE ZOOLOGICAL REGIONS 309 

walrus, hunted for his ivory tusks, which are superior to those of the elephant, 
and the narwhal, or sea unicorn, whose ivory horn is eight or ten feet in 
length. 

Various depths are suited to various species of marine animals. The reef- 
building polyp cannot flourish at a greater depth than about 150 feet below 
the surface. Lower down, in depths so great as 1500 or even 2400 fathoms, 
living forms are found, but they are of a low order— foraminifera, spo'nges, 
starfish, and mollusks. The bathymetrical range of such creatures is surpris- 
ingly great. 

The Floras of the Zoological Regions. — The flora of each 
region may not perhaps be so distinctly marked as the fauna. 




West Indian Boa 
From photograph. Used by permission of the New York Zoological Society. 

There will naturally be much overlapping, many species being 
very widely diffused, and some being common to all parts of the 
globe. Still, we ought to find some characteristic floral peculi- 
arities in each region. 

The Old World region is the native home of all the cereals 
excepting maize, of the apricot, the cherry, the apple, the pear, 
the olive, the cork oak, and sycamore fig. 

The Ethiopian region has among its pecuHar vegetable forms 
the baobab, the oil palm, and coffee. 

The Indian region is characterized by the banyan, the fig, the 
mango, cinnamon, the guttapercha and teak trees, and the sweet 
potato. 



310 THE DISTRIBUTION OF ANIMALS 

The Australian region has a flora very distinct from that of 
all others. The leaves of the trees are of a peculiar bluish green 
hue, and strangely present their edges to the sun, arranging 
themselves vertically instead of horizontally. The eucalyptus 
or gum trees, of which there are 400 varieties, are probably 
the loftiest trees in the world. Many are 400 feet high. One 
monster was felled which measured 480 feet. The beefwood 
trees are remarkable. Instead of leaves, of which they have 
none, they have sheaths inclosing their branches. They thus 
resemble in structure the "horsetail" with which we are 
familiar. 

The NortJi Avierican region is the native home of the mag- 
nolia, the live oak, the Sequoia gigantea (giant trees of Cali- 
fornia), and persimmon. Nearly 400 species of trees are 
peculiar to this region. 

The South American region is distinguished by the multi- 
tude of its parasitic forms. Peculiar to it are the cinchona, the 
cacao, the manioc, the potato, the sarsaparilla, the Victoria Regia, 
and the passion flower. 



XXIX. MAN 

Range of Human Habitation. — Man dwells in every zone and 
at nearly all altitudes. He is literally cosmopolitan. Unlike the 
irrational animals, he can to a large extent overcome the force 
of external conditions. He can protect himself from the severity 
of the winter's cold, and maintain his existence amid the snows 
of the Arctic regions ; and on the other hand he can endure the 
fierceness of intertropical heat. Thus his horizontal range is 
almost unlimited. 

He has, again, an ample vertical range. The lowest place 
where men have established permanent dwelling places is in the 
valley of the Dead Sea, 1 300 feet beloiv the sea. The highest 
is at the convent of Hanle, inhabited by twenty Tibetan monks, 
16,533 feet above the sea. These limits include a vertical range 
of more than three miles. 

The Unity and Diversity of the Human Family. — Wherever 
Man is found, he presents the same essential features of body and 
of mind. No such differences sunder men as those which exist 
between the horse and the lion, the eagle and the ostrich. The 
human family is of one blood. 

Still the heat and cold to which man is habitually exposed, the 
food upon which he lives, and the physical conditions generally 
by which he is surrounded will, in the lapse of time, produce 
certain effects upon his bodily and intellectual organization. 
Hence we find wide diversities characterizing different portions 
of the human family. Men differ in color, in feature, in mental 
and moral peculiarities, industrial habits, social and govern- 
mental institutions. 

Division into. Races. — Some ethnologists divide the great 
human family into three, some into five, others into six or even a 
larger number of races. 




(312) 




JL. L. POATES ENGR;G CO., N. Y. 

(313) 



314 



MAN 



The five great races of mankind, as generally recognized, 
are the Caucasian or white, the Mongolian or yellow, the Negro 
or black, the Malay or brown, and the Indian or red. 

The Caucasian Race derives its name from the Caucasus range 
of mountains, because of the tradition that the region traversed 
by these mountains was the birthplace of the race. 

The chief divisions of the Caucasians are: (i) the Indo- 
European, comprising the Hindus, Persians, Circassians, Sla- 
vonians, Teutons, and 
Celts; and (2) the Se- 
mitic families, of whom 
the Hebrews and Arabs 
are the most important. 

The term Indo-European 
is derived from the fact that 
this division of the race has 
established itself all the way 
from India to the farthest 
bounds of Europe. 

Nine tenths of the peo- 
ple of the United States, 
as well as all the peoples 
of Europe, except the 
Lapps, Finns, and Mag- 
yars, and the Turks 
proper, belong to the 
Caucasian race. Both of the Americas are governed by it. 
Africa is controlled by it. In Asia, it dominates from the shores 
of the Mediterranean, through Arabia, and Persia, and along the 
southern slopes of the Himalaya Mountains beyond the banks 
of the Brahmaputra. 

The Caucasians are the most symmetrical in figure, comely in 
person, and beautiful in feature, of all the branches of the human 
family. The numerous divisions and subdivisions of the race 
vary in complexion according to the region they occupy. The 
extremes are the Germans with their flaxen hair, blue eyes, and 




Caucasian 



THE MONGOLIAN RACE 



315 






fair skin, and the Hindus with raven locks, black eyes, and olive- 
brown or brownish black skin. The face of the Caucasian is 
oval, the head ample ; the hair full and often curled or wavy. 

In intellect this race ranks first. With very few exceptions 
all the leading thinkers of the world have been Caucasians ; and 
without any exception all the great discoveries of recent times 
have been made by members of this family. 

To this race has been assigned the task of civilizing and 
enlightening the world. 
Its social habits and its 
governmental institu- 
tions, its educational sys- 
tems and its religious 
views, are those which 
most conduce to the ele- 
vation and happiness of 
mankind. 

Wherever the white 
man establishes himself 
he speedily becomes 
dominant; while the com- 
munities of other races 
into which he introduces 
himself are commonly 
subjected to a gradual 
process of extinction. 

The Mongolian Race derives its name from the Asiatic tribe 
of Mongols. The Chinese, Indo-Chinese, Japanese, Tibetans, 
Samoyedes, and Turks in Asia, the Finns, Magyars, and Lapps 
in Europe, and the Eskimos of the Arctic regions of North 
America are branches of this race. 

The color of the Mongolian is olive-yellow. His face is 
broad, with wide and flattened nose, and small, obliquely 
set eyes. His hair is straight, coarse, and black. In stat- 
ure he is somewhat below the ordinary standard of the 
Caucasian. 





Mongolian 



3i6 



MAN 



In intelligence and moral character he ranks next to the 
Caucasian. 

Branches of the Mongolians, as the Eskimo, are very low in 
the intellectual scale. Not so the Chinese and Japanese. It is 
true that, in the past, they have displayed the mental inactivity 
which marks the Mongolian in general. They remained for 
ages just where their ancestors had been. A great change, 
however, is going on. The establishment of a constitutional 

form of government by 
the Japanese, and their 
adoption of many im- 
portant features of 
European civilization, 
entitle them to rank 
among the progressive 
nations of the world. 

The same may be said 
in a less degree of the 
Chinese. 

Somewhat also must be 
said in commendation of the 
native civilization of both tliese 
great Mongolian communities. 
China has had a governmental 
system, including the feature 
of promotion by competitive 
examinations, which has stood 

the test of ages. Japan, too, has been a prosperous and well-ordered state for 

generations of which we have no count. 

In religion the Mongolians are generally Buddhists. 

The Negro Race is so called from the color of its skin (Latin, 
niger, black). It occupies nearly the whole of the African 
continent. The hair of the Negro is short and curly ; his nose 
is flat, wide, and upturned; his cheek bones are prominent, and 
his lips thick. 

The moral and intellectual status of the Negro in his native 
land is low. When brought into contact, however, with the 




Negro 



THE MALAY RACE 



317 



Caucasian race, he shows himself capable of considerable ele- 
vation. 

The native Australians, though classed by some ethnologists as a separate 
race, may properly be regarded as a branch of the Negro family. They are 
probably the most degraded members of the human species. Before the 
European settler they are rapidly dying out. 

The Malay Race is held by some to be a branch of the 
Mongolian. Its characteristics are, however, sufficiently marked 
to entitle it to separate 
classification. 

The Malays occupy 
a part of southeastern 
Asia and most of the 
islands of the Pacific. 
The Malay peninsula, 
Sumatra and Java, 
Borneo, Celebes, For- 
mosa, the Phihppines, 
New Zealand, and the 
Polynesian Islands, all 
had this race for their 
aborigines. 

The members of the 
Malay race are of 
medium height, with 
well-proportioned limbs. 

Their color varies from olive-yellow to brown or black, 
hair is coarse and black. 

Intellectually and morally the Malayan is of a low order. 
Some of them, however, have a written language and a legal 
code. They are true sea rovers, and prone to piracy. 

The American Indians constitute what some ethnologists 
designate as an offshoot of the Mongolian race. At the time 
of Columbus they had spread all over North and South 
America. 

Some of the better known tribes are the Chippeways, Da- 




Malay 



Their 



3i8 



MAN 



kotas, Apaches, and Cherokees in North America ; the Caribs, 
the Araucanians, and Patagonians in South America. 

The American Indian is copper-colored or red, and therefore 
he is often called the Red man. His hair is black, coarse, and 
straight, his cheek bones prominent. In person he is tall and 
lithe. He is remarkable for his endurance of fatigue and his 
disregard of pain. Intellectually and morally he occupies a 

medium position among 
the races of mankind. 

The Incas of Peru and the 
Aztecs of Mexico were found 
in a comparative]}' high state 
of civiHzation by Pizarro and 
Cortez ; and there are, in 
Central America and in New 
Mexico and Arizona, interest- 
ing memorials of a long-for- 
gotten civilization which had 
its home in those regions. 

The Montezumas of Mexico 
had their halls, their acade- 
mies and schools, their zoo- 
logical and botanical garden.s, 
their calendar and their monu- 
ments. Their capital, at the 
time of Cortez, vied with the 
American Indian wealthiest cities of Europe. 

Conditions Favourable to Civilization. — From this brief re- 
view of the races it will be seen how powerful has been the 
influence of physical circumstances upon Man. Some portions 
of the human family have remained hopelessly barbarous. 
Some have received civilization from others, and some, again, 
have originated a civilization of their own — an indigenous civi- 
lization. Wherever this last has occurred, it has invariably 
been neither at the poles, nor in the hot lands of the tropics, 
but rather in a middle ground between the two. It is here 
that conditions best adapted to man's physical development 
are found. 




MAN'S INFLUENCE UPON PHYSICAL GEOGRAPHY 319 

An indigenous civilization has never had its origin under the 
bHghting blasts of the Arctic regions. Life there, from the 
cradle to the grave, is a continuous struggle for mere sub- 
sistence. The body is so pinched and starved by cold and 
hunger as to prevent the development of the mind. 

Neither do the moist and overheated climates of the torrid 
zone appear to be favorable to mental development. There 
the rainy season and the constant heat dwarf and enervate the 
body. Cold may not pinch, nor hunger gnaw, yet fever racks the 
frame ; and the mind, in its first -and feeble steps toward civiliza- 
tion, is crippled by the ills of the body. Body and mind, more- 
over, lack in the torrid zone, by reason of its superabundant 
productiveness, the great stimulus to human exertion, — necessity. 

Man, to be civilized, must be beyond the reach of climatic 
extremes. 

Man's Influence upon Physical Geography. — While, however, 
we notice the influence of physical geography upon Man, we 
must also notice the influence of Man upon physical geography. 
Although, like the brutes, he is strongly impressed by his 
material surroundings, he is unlike the brute creation in this : 
They cannot modify the conditions which surround them ; he 
can. The methods to which he resorts are mainly three : 
(i) Drainage, (2) Irrigation, (3) Extension of the range of useful 
plants and animals. 

In many cases skill and perseverance triumph over natural 
difficulties that seem insuperable. 

Immense changes are wrought by artificial drainage. Super- 
fluous water, instead of being left to form marshes, saturate 
the soil, and be taken up by evaporation, is carried off under- 
ground through the drain pipes ; consequently, the air is not 
so largely impregnated with moisture as formerly, and the soil, 
instead of being constantly chilled by evaporation, is rendered 
warm, genial, and productive. 

This result is particularly noticeable in England and Scot- 
land, where very extensive areas have been drained and 
brought under cultivation. 

M.-S. PHY. GEO. — 19 



320 MAN 

Holland has been reclaimed from the sea. The water has been diked out ; 
and many parts of the country that were the bottom of the sea are now dry 
land, and though below the level of the sea, form the home of industrious and 
happy communities. 

Years ago there were along the lower banks of the Mississippi, subject to 
overflow, and uninhabitable, " drowned lands," embracing an area larger in 
the aggregate than the state of New York. Many of these lands have been 
reclaimed by means of levees. 

1 he dike lands of Nova Scotia and New Brunswick have been reclaimed 
from the sweeping tides of the Bay of Fundy. They are probably the finest 
hay lands in the world. Some of them have been cropped 200 years. They 
are as sure to yield as the fields of Egypt. 

By Man's agency in using the waters of the Nile for irrigation, 
Egypt became in olden time the granary of the world. Canals 
conveyed the water to lands not reached by the flood. And 
to-day the Egyptian peasant is using with profit the devices 
employed by his ancestors more than 3000 years ago. Sharply 
contrasted with these, as a result of modern engineering, is the 
great dam at Assuan by which an ample water supply, for irri- 
gating purposes, has been afforded to a large territory. Much 
of the country yields three crops every year. 

In India and Ceylon vast districts of country are rendered fer- 
tile by the use of reservoirs, constructed ages ago for collecting 
water in the rainy season, but even on a larger scale by the 
gigantic systems of irrigation constructed by the English. 

The dry regions of our own country also are now largely 
irrigated. In Utah, California, Arizona, New Mexico, and other 
far Western states the wilderness has been, by this means, trans- 
formed into a garden. Some single " canals " with their distrib- 
uting channels carry water to 150,000 acres. 

Races of men, species of animals, and families of plants have 
been carried from one country to another, and their geographi- 
cal range enlarged. 

Indian corn, tobacco, and the potato, with many other plants, 
the turkey, and other animals, were indigenous to America. 
They have been carried to the Old World and acclimated. On 
the other hand, the horse and cow, the sheep, hog, goat, ass, and 



MAN'S INFLUENCE UPON PHYSICAL GEOGRAPHY 32 1 

other animals of the Old World, with wheat, oats, rye, barley, and 
rice, the sugar cane and coffee, and a great variety of other 
plants have been transported to America. 

A few stray cattle and horses, escaping to the pampas and 
llanos of South America, multiplied exceedingly. So wonderfully 
did they increase that, upon the pampas, they were slaughtered 
by millions for their hides, horns, and tallow. 



XXX. GEOGRAPHICAL DISTRIBUTION OF LABOR 

Distribution of Labor Dependent on Physical Geography. — 

Every nation has industries peculiar to itself. These, to a large 
extent, have their root in geographical circumstance, or in dif- 
ference of climate. 

To show how human labor, when unaffected by tariffs and 
untrammeled by legislation, would naturally distribute itself 
over the earth in obedience to geographical law, let us suppose 
two families to have been planted originally on the earth, one 
at the equator, the other in the Arctic regions. How different, 
on account of their geographical surroundings, would be their 
occupations ! 

The intertropical family would seek the shades of the groves, 
pluck the ripe fruit overhead, require little clothing, and be ex- 
empt from undergoing the hardships of toil to earn their daily 
bread. With little exertion on their part nature would supply 
their wants. 

The Arctic family, on the contrary, would be clothed with skins 
and furs ; the earth would produce no grain or vegetables for 
them. They would live by the chase and the bounties of the 
sea. 

Now, suppose these two families gradually extend to themselves, 
the one toward the north, the other toward the south, meeting 
midway near the isotherm of 50°. 

The occupations of both, as they continued to approach this 
middle ground, would no longer be directed, on one side mainly 
toward the sea, and on the other exclusively to the soil ; but 
would become more and more diversified. 

The necessities of the southern family would compel them to 
resort to sundry active occupations, some to the manufacture of 
clothing, others to the fabrication of implements for husbandry ; 



INDUSTRIES OF THE UNITED STATES 323 

Others again to seafaring. Novel opportunities would present 
themselves to the northern community, and induce them like- 
wise to subdivide their labor. They would divert a portion of 
it from the sea and the chase, and devote themselves to a 
greater or less extent to agriculture, to the forest, the mine, and 
the factory. 

Such a diversity of occupation really exists among men. 
The middle latitudes, embracing regions lying not far from the 
isotherm of 50°, form a belt encircling the earth, where human 
occupations are most diversified. In some parts of this belt the 
tending of flocks and herds and the raising of stock are the 
chief industrial pursuits ; in other parts agriculture, in others 
mining, manufacturing, seafaring, and lumbering ; in some, all 
of these occupations, or several of them, are combined. 

To the south of this middle ground, the attention of the people 
is devoted more and more to the field and the forest ; to the 
north, more and more to hunting and the sea. 

Along this middle ground are found the most active seafaring 
and commercial peoples in the world, the greatest manufactur- 
ing nations, and the largest cities. « 

Within its belt are included most of the United States, Japan, 
the populous parts of China, and all the great commercial, min- 
ing, and seafaring communities of Europe. 

It is now easily perceived that there are geographical reasons 
why the people of South America, of Africa, India, and of the 
tropical and subtropical regions of the earth should, in the main, 
be agricultural or mining in their industries rather than seafar- 
ing or manufacturing. 

In general it may be laid down as a rule, that the industries 
of every country are connected with its geography, and that 
human labor is distributed, largely, in obedience to certain phys- 
ical conditions. 

Industries of the United States. — A brief survey of the indus- 
tries of our own country will serve well to illustrate this law of 
the geographical distribution of labor. 

Let us observe in the first place how the principle applies to 



324 GEOGRAPHICAL DISTRIBUTION OF LABOR 

our various agricultural pursuits. Climate, of course, furnishes 
the predominant reason why different products are raised in 
different parts of the country. But we shall notice that other 
minor causes are not without their influence. In the valley of 
the Mississippi, which may be regarded as the great agricultural 
region, there is found as we advance northward from Louisiana, 
a succession of climatic belts, and a corresponding variety of 
crops engaging the attention of the husbandman. 

First of all, near the borders of the Gulf of Mexico, comes a 
belt in which sugar and rice are important crops. Leaving this 
belt, we enter regions, one after another, specially adapted to 
the cultivation of cotton, tobacco, corn and wheat, hemp, the 
grape, and orchard fruits. 

If the journey lie along the Atlantic slope from Florida to 
Maine, we find a similar succession of belts and products ; but 
with this striking difference, owing to the influence of the sea, 
namely, that the climates are milder and the belts broader. 

In the " Tide-water Country " these belts are so widened that 
rice cultivation is carried up into North Carolina, cotton is raised 
in Virginia, and figs in Maryland — all much farther north than 
on the west of the Alleghanies. 

In the tide- water country of Georgia and the CaroHnas, rice 
is an important article of cultivation. There is a geographical 
reason for this. Rice fields, in certain stages of the crop, must 
be flooded, for which purpose the tidal creeks and rivers of the 
seaboard afford excellent facilities. 

At the same time Louisiana has become the first rice-growing 
state in the Union. In the Mississippi delta the river is high 
above the cultivated ground. Consequently a supply of water 
can be obtained by simply tapping the river. In the southwest- 
ern parishes, away from the river, and on the coastal plain of 
Texas, large areas of low and level lands are irrigated from sur- 
face reservoirs and wells. 

The agricultural pursuits of the Pacific slope, owing to its 
physical peculiarities, differ from those of the Atlantic. No rice 
or cotton is cultivated. But the region is unsurpassed for its 



INDUSTRIES OF NEW ENGLAND AND GULF STATES 325 

wheat and fruit crops ; the olive, vine, and orange yield abun- 
dantly, while stock raising and wool growing are profitable 
employments. 

Considering now the various other industrial pursuits of our 
people, we find it to be the rule that Physical Geography has 
largely determined how the occupants of each section shall 
employ themselves. 

Here we view far-reaching grass-covered plains which naturally 
suggest the occupations of stock raising, dairying, or wool grow- 
ing. Elsewhere we traverse forests famed for lumber, ship " 
timber, and naval stores. In yet another region we observe that 
attention is directed to the great lakes or water courses for fish 
and fowl ; or to the interior of the earth for minerals ; or to 
commerce, manufacturing, and navigation. 

All these occupations are, it is true, adopted according to 
individual fancy, yet they are clearly prompted and controlled 
by geographical influences. 

Industries of New England and Gulf States Contrasted. — 
A very striking illustration of the law of geographical distribu- 
tion of labor is obtained when we contrast the leading occupations 
of such widely separated sections of our country as the Gulf 
states and New England. 

In the former there is no "wintry weather." The husband- 
man may labor in the field all the year long, and the soil yields 
abundantly. 

In New England, on the other hand, the ground is covered 
with snow, or is frozen hard, during four or five months in the 
year. How is New England industry to ply its hand during this 
period .-' It cannot till ; neither can it stand idle. 

Forests upon the mountains, ships upon the sea, quarries of 
valuable stone, and above all factories of every description fur- 
nish ample employment for the industrious population. New 
England is preeminently devoted to manufacturing. Its polished 
granites and marbles are distributed everywhere along the At- 
lantic seaboard for building and ornamental purposes ; its manu- 
factures find a market in every part of our own country and are 



326 GEOGRAPHICAL DISTRIBUTION OF LABOR 

exported to the far-distant seaports of China and Japan and the 
islands of the seas. 

Louisiana, and her sister Southern states, on the other hand, 
want laborers for their harvests of cotton, corn, sugar, rice, naval 
stores, hemp, tobacco, etc. There are, therefore, inducements 
peculiar to each of these two sections which allure the people of 
one to this branch of industry, the people of the other to that, 
according to geographical conditions. In one, these inducements 
lead to the sea and the factory; in the other, they point to the 
bosom of the earth. 

Mining and Manufacturing. — If coal and .the useful metals are 
found in any region, manufacturing interests will sooner or later 
be developed. It is in no small degree owing to her vast deposits 
of coal and iron that Great Britain occupies her extraordinary 
position as a manufacturing nation. Pennsylvania, Ohio, Ala- 
bama, Illinois, the Virginias, Maryland, Michigan, and other 
states similarly rich in the useful minerals, are actively engaged 
in mining and metallurgy. 

Fishing and Commerce. — Again, people are maritime in their 
habits from physical reasons ; partly because they are adjacent 
to the sea, and partly because, owing to the conditions which sur- 
round them, the bounties of the sea are to them more enticing than 
thebounties of the land. Hence it is found that the seafaring 
populations of the world belong chiefly to those countries where, 
either from the poverty of the soil, the severity of the climate, 
or the high price of food, it is easier for some of the population 
to make a living by braving the sea than by delving on shore. 

Ships at sea are not manned by sailors from the Mississippi 
Valley and the Southern states, where lands are cheap, climates 
mild, and where the soil is lavishly kind ; but rather by men 
from New England, Great Britain, and the countries of north- 
western Europe, where, largely on account of geographical con- 
ditions, the laborer finds it in many cases easier to make a living 
at sea than on shore. 

Commerce originates between nations to satisfy needs. Arti- 
cles required for food and shelter, comfort or luxury, being 



FISHING AND CO\niERCE 327 

irregularly distributed over the globe, it becomes necessary that 
human industry should be partly directed to the exchanging of 
the natural and artificial products of one region for those of 
another. To this end many routes of commerce have been es- 
tablished, necessitating the investment of great capital in rail- 
roads, steamships and other vessels, and at the same time giving 
employment to a vast multitude of people. 



APPENDIX 



XXXI. PHYSICAL GEOGRAPHY AS A SCIENCE 

Scope of Physical Geography. — The earth is not young. 
Like a living being, it is a product of evohition or growth. In 
the course of its development it has passed through many 
stages. The interaction of sea and land, rock decay and denu- 
dation, transportation and deposition of sediment, vulcanicity 
and glaciation, elevation and subsidence, earth folding and fault- 
ing, animal and plant life, have all contributed to its present 
form. Yet the earth as we know it is not a finished product ; 
change and remodeling are still taking place ; the forces of the 
past, in varying degree, are still at work. It is, however, as the 
abode of man, chiefly, that the earth merits our attention. The 
relation of man to his environment or surroundings is a practical 
matter, and should we define Physical Geography as the study 
of the earth and its phenomena in the present stage of their 
existence with special reference to that relationship, we have 
before us a field of the widest scope. 

The Relation of Physical Geography to Other Sciences. — It is 
only by a knowledge of the earth in its present condition that 
Man has been able to interpret its past history. Physical 
Geography is, therefore, a most important adjunct to geology. 
Indeed, there is no well-marked line of division between these 
sciences which, in many instances, occupy common ground. 
Geology, however, is usually confined to a consideration of the 
history of the earth and its inhabitants as recorded in the rocks. 
But this seems arbitrary in view of the fact that the earth is a 
unit. It were better that Physical Geography should constitute 
the latest chapter of geology. 

328 



HOW PHYSICAL GEOGRAPHY SHOULD BE STUDIED 329 

Like geology, Physical Geography rests upon a foundation of 
other sciences. To explain the phenomena of the earth it has 
oftentimes been necessary to invoke the assistance from astron- 
omy, chemistry, physics, zoology, botany, and mineralogy ; for 
the earth is one of the planets, it consists of matter, it is in- 
habited by animals and plants, and is, -for the most part, com- 
posed of mineral matter. 

How Physical Geography should be Studied. — ^ In the ele- 
mentary study of Physical Geography the text-book occupies an 
important position. Not only is" such a work a record of the 
observations and conclusions of those who have made a specialty 
of earth phenomena, but also a manual of guidance for those 
who desire to acquaint themselves with the subject. Moreover, 
at the outset the student should understand that although the 
ability to memorize a text may add much to his information, 
it is by no means an index of his scientific attainments. If 
the best results are to be obtained from the study of Physical 
Geography, he should, as far as possible, verify the data and 
conclusions of the author. By training of that kind he may 
become competent to make independent observations and from 
them deduce proper conclusions. Then, and not till then, has 
he reached that degree of culture which is truly scientific. 
His local or home surroundings become now an ever-present 
field of research. Nowhere in the world is the opportunity 
for geographic investigation denied him. Lines of investiga- 
tion open in many directions : He may observe winds, clouds, 
rainfall, temperature, and other weather conditions and note 
their bearing upon climate ; he may study the effects of rock 
weathering or decay and the topographic features arising from 
erosion ; he may face the problems of stream dissection, current 
action, delta formation, cascades and waterfalls in the rill 
formed by a passing shower ; he may learn something of 
Nature's processes by observing the effects of storms and 
floods. These and many other fields of inquiry equally inviting 
lie within the reach of all students. Furthermore, every local- 
ity has its special phenomena : For example, wave action may 



330 PHYSICAL GEOGRAPHY AS A SCIENCE 

be studied by those living upon the sea coast or near lakes and 
ponds ; ice action by those living in the colder regions of the 
earth; glaciers and glacial motion by those living in Alpine 
regions ; and vulcanicity and earthquakes by those living in 
volcanic regions or parts of the earth subject to crustal disturb- 
ances. 

Maps, Models, and Other Illustrative Materials. — There are, 
however, fields of geographic inquiry which ordinarily lie be- 
yond the reach of most students, as the expense of investigation 
is too great or the region to be examined too remote or too 
inaccessible. To this class belong deep-sea research, electro- 
magnetic observations, Arctic exploration, the investigation of 
high mountain ranges, the exploration of desert regions, and 
the like. Such forms of research can be carried on only under 
the auspices of the government or of well-endowed private 
institutions. The student of geographic tastes should embrace 
every opportunity to travel. There are problems worthy of his 
best thought and effort within the boundaries of his own state. 
But for the elementary student this also is usually impracticable, 
hence the necessity of a geographical collection in every school 
or college. This should include a set of the most recently 
published maps of the continents ; a good atlas, selected folios, 
atlas sheets and charts from the publications of the United 
States Geological Survey and the United States Coast Survey ; 
relief models of the continents ; the Harvard Geographical 
Models ; and a relief globe such as the Jones Model. In ad- 
dition, if possible there should be included a set of lantern 
slides or photographic views. Such illustrations, are extremely 
valuable to the student, as they convey to him an exact im- 
pression of the region or phenomena under consideration. 
He should, moreover, have access to other books than the 
text, but their number will depend upon the resources of the 
individual or the school. 

In higher institutions a similar equipment, but in an enlarged 
form, should constitute the furnishings of a geographic labora- 
tory. Here the number of relief maps and models should be 



MAPS, MODELS, AND OTHER ILLUSTRATIVE MATERIALS 33 1 

greatly increased, especially by the addition of duplicates of the 
many excellent models prepared under the auspices of the 
United States Geological Survey and other departments of 
the national government. The collection of maps should also 
be made more complete, and embrace not only political, but 
topographic and geologic maps as well. If not found in other 
departments of the institution, some of the more common in- 
struments for weather observation should be added, such as a 
mercurial or aneroid barometer, a themometer, a vane, anemom- 
eter, and rain gauge. This laboratory should be furnished 
with tables suitable for map work, cabinets for the storage of 
maps, photographs, and other geographic matter. While the 
facilities afforded by such a laboratory may increase many fold 
the value of Physical Geography as a study, they do not sup- 
plant the necessity of actual observation in the field. 



INDEX 



Abyssinia, plateau of, 123. 

Aconcagua, 48. 

Active volcanoes, 50. 

Adirondack Mountains, 104. 

^pyornis, 306. 

Africa, drainage of, 169, 170. 

rainfall of, 252. 

relief of, 123-126. 
Agonic lines, 38. 
Agulhas current. 197. 
Air, currents of, 219. 

moisture of, 239. 

weight of, 202. 
Alaska, climate of, 213. 
Albacore, 30S. 

Alcohol in thermometers, 208. 
Aleutian current, 196. 
Alexandria, 25. 
Algae, in hot springs, 42. 

sea forms of, 2S7. 
Allegheny plateau, 107. 
Allspice, 290. 
Alluvial plains, 78. 
Alpaca, 301, 304. 
Alps, 114-116. 
Altai Mountains, 121. 
Amazon River, no. 

description of, 167. 

no delta, 150. 
Andes Mountains, 107-109. 
Anemometer, 218. 
Angle of dip, 36. 
Animal life, zones of, 292. 
Animals, aquatic, 307. 

distribution of, 292. 

higher, 286. 

lower, 281. 

modified by climate, 283. 



Antarctic drift, 196, 197. 
Antarctic Ocean, 174. 

currents of, 195. 
Anticline, 87. 
Anti-cyclones, 232. 
Antisana, 108. 
Anti-trades, 221. 
Apennines, 117. 

Appalachian Mountains, 104-107. 
Apple, 309. 
Apricot, 309. 
Apteryx, 305. 
Aquatic animals, 307. 
Arabia, 121. 
Aral, Sea of, 160, 161. 
Ararat, 121. 
Arctic Ocean, 173," 174. 

currents of, 195. 
Argon, 200. 
Argus pheasant, 298. 
Arica earthquake, 64. 
Arid region, erosion in, 84. 
Armadillo, 301. 
Armenia, 121. 
Artesian wells, 142-144. 

temperature of, 41. 
Artificial magnet, 32. 
Ash trees, 291. 
Ashes, volcanic, 50, 53. 
Asia, drainage of, 169. 

relief of, 11 9-1 23. 
Asia Minor, 121. 
Ass, 301. 
Asteroids, 10, 12. 
Atlantic coast tides, 188. 
Atlantic drift, 213. 
Atlantic highland, 104-110. 
Atlantic Ocean, 174-178. 



333 



334 



INDEX 



Atlantic Ocean, currents of, 193, 194. 
Atlas Mountains, 123. 
Atmosphere, 70. 

circulation of, 219. 

composition of, 200. 
Atmospheric electricity, 275. 
Atmospheric pressure, 202. 
Atmospheric temperature, 206. 
Atolls, 132-135. 
Attractive power of earth, ^;^. 
Aurora australis, 277. 
Aurora borealis, 276. 
Australia, flora of, 310. 

great barrier reef, 132. 

relief of, 126, 127. 
Australian Alps, 126, 127. 
Australian current, 196. 
Autumnal equinox, 27. 
Avalanche, 260. 
Axis of the earth, 23. . 

direction of, 25. 
Axis of elevation, 95. 

Baboon, 296. 

Bad lands, 84. 

Baikal, Lake, 164. 

Balkan Mountains, 116. 

Balsams, 291. 

Baltic Sea, chmate of, 213. 

saltness of, 172. 
Bamboo, 291. 
Banana, 289. 
Banyan, 309. 
Baobab, 309. 
Barbary lion, 296. 
Barley, 288. 

Barometer, mercurial, 203. 
Barrier islands, 182. 
Barrier reefs, 132. 
Bars, 148. 
Basin, 165. 
Basins of geysers, 43. 
Bath, temperature of springs at, 41. 
Bay of Fundy, tides in, 188. 
Bear, 292, 296, 297, 299, 302. 



BeefvvTood tree, 310. 

Belted coastal plain, 78. 

Bepho, 272. 

Beverage plants, 290. 

Bird of paradise, 298. 

Birds, 292, 300. 

Bison, 299. 

Black Stream, 196. 

Blanc, Mont, 116. 

Block mountains, 88; 102, 104. 

Blue crov^r, 299. 

Blue jay, 299. 

Blue Mountains, Australia, 126. 

Boa-constrictor, 301, 309. 

Bolivian plateau, 82, 108. 

Benito, 308. 

Bonneville, Lake, 103, 162. 

Boothia, 34. 

Bores, 189. 

Bower bird, 298. 

Bowlders, transported, 268. 

Bowlders of transportation, 268. 

Brahmaputra, delta of, 79. 

Brazil current, 193. 

Brazilian highland, 109. 

Breadfruit, 289. 

Breadth of wave, 179. , 

Breakers, 179, 180. 

Breezes, land and sea, 224. 

Bridge of Sighs, 99. 

British Channel, tides in, 189. 

British Columbia, chmate of, 213. 

British Islands, 129. 

Broken plateaus, 83. 

Brown bear, 292. 

Budapest, temperature of well at, 41. 

Bustard, 296. 

Cacao, 290, 310. 

Caldera, 29, 161, 162. 

California earthquake, 63, 66, 68, 

69. 
Calms, belt of, 223. 

of Cancer, 223. 

of Capricorn, 223. 



INDEX 



335 



Calumet-Hecla mine, temperature of, 

40. 
Camel, 292, 296, 302, 303. 
Campagna, 165. 
Cancer, Tropic of, 30. 
Canyon, 91. 

Capricorn, Tropic of, 31. 
Caracas earthquake, 65. 
Carbon dioxide, 200. 
Carbonate of lime, 42. 
Carnivorous animals, 282. 
Carpathian Mountains, 116. 
Carson Lakes, 103. 
Cascade, 151. 
Cascade Mountains, 100. 
Caspian Sea, 123, 160, 161. 
Cassava, 290. 
Cassiquiare River, no. 
Cassow^ary, 298, 305. 
Castor oil, 291. 
Catskill Mountains, 104. 
Caucasian race, 314. 
Caucasus, 116. 
Cayambe, 108. 
Cayuga Lake, 156, 160. 
Cedars, 291. 
Centigrade scale, 209. 
Centrifugal force, 20, 184. 
Centrosphere, 22. 
Cervin, Mont, 85. 
Chaco, III. 
Chain, mountain, 85. 
Chamois, 305. 
Change of seasons, 29. 
Charleston earthquake, 63. 
Cherry, 309. 
Chestnut, 291. 
Chimborazo, 47, 48, 109. 
Chimpanzee, 293. 
China, plains of, 123. 
Chinchilla, 301, 305. 
Chottes, 126. 
Cinchona, 291, 310. 
Cinnamon, 290, 309. 
Circulation, oceanic, 197. 



Circulation of the atmosphere, 218, 
219. 

of water, 139. 
Cirques, 100. 
Cirro-cumulus cloud, 244. 
Cirrus cloud, 242, 244. 
Civet, 297. 
Civilization, 318. 
CHmate, 210. 

afifected by ocean currents, 212. 

affected by winds, 212. 

at Werchojausk, 212. 

continental, 211. 

inland, 211. 

insular, 211. 

maritime, 211. 

of Alaska, 213. 

of British Columbia, 213. 

of Cuba, 216. 

of England, 213. 

of Labrador, 213. 

of Norway, 213. 

of Oregon, 213. 

of Orizaba, 216. 

of Sahara, 212. 
Climatic belts, 324. 
Clothing, plants used for, 291. 
Cloud, definition of, 243. 
Cloud Ring, 254. 
Clouds, classes of, 244. 

formation of, 201. 
Cloves, 290. 
Coast line, 72-74. 
Coastal plains, 76. 
Coffee, 290, 309. 
Colorado, Grand Canyon of, 91. 
Colorado Plateau, 104. 
Columbia Plateau, 100. 
Coma, 12. 
Comets, 10, 12. 
Commerce, 326. 

Comstock lode, temperature of, 40. 
Condensation of water, 138, 139, 240. 
Condors, 301, 303. 
Conduction, 207. 



336 



INDEX 



Constant rains, 254. 
Constant winds, 221. 
Continental climate, 211. 
Continental elevation, 91. 
Continental islands, 128, 129. 
Continental relief, 95. 
Continents^ 70. 
Contraction, effects of, 86. 
Convection, 206. 
Coral islands, 130-135. 
Coral vi^ind, 178. 

reefs, 131, 132, 197. 
Corals, 308. 
Cork oak, 309. 
Corn, 324. 
Corncrake, 296. 
Coronado Beach, 179, 180. 
Cotidal lines, 186. 
Cotopaxi, 47, 50, 108. 
Cotton, 291, 324. 
Counter current, 192. 
Counter trades, 221. 
Cow, 292, 296. 
Crater, 46. 

Crater Lake, 156, 161 
Craters, basins of, 43. 
Crest, mountain, 86. 
Crest of wave, 179. 
Crevasse, 266. 
Crimson lory, 298. 
Crocodiles, 292. 
Crumpling, 86. 
Cuba, climate of, 216. 
Cumulo-stratus, 245. 
Cumulus, 243, 245. 
Curassows, 301. 
Current, Arctic, 213. 
Currents, ocean, 192-197, 212. 
Curvature of the earth, 18. 
Cut-off, 147. 
Cyclones, 229, 230. 

Dangerous archipelago, 133. 
Danube River, deltas, 149. 
jetties of, 148. 



Date palms, 285. 
Day, lunar, 183. 

sidereal, 28. 

solar, 28. 
Day and night, lengths of, 26. 
Dead Sea, 123, 159, 160. 
Deccan, 121. 
Dechnation, magnetic, 37. 

of the needle, 36. 

variations in, 38. 
Dee, tides of the, 189. 
Deer, 296. 

Deficient rainfall, 255. 
Deformation, crustal, 93. 
Delta, 78, 149. 
Delta plain, 79. 
Delta shore lines, 79. 
Dembea, Lake, 123. 
Density of the earth, 21. 
Denudation, 77. 
Deposition, 146-150. 
Desert plateaus, 85. 
Deserts, regulators of rainfall, 252. 
Dew, 241. 

Diastrophic plateaus, 82. 
Diatoms, 178, 286. 
Dip of strata, 70, 78. 
Dip of the needle, 34. 
Dipper, 24. 

Dissected plateaus, 83. 
Distributaries, 149. 
Distribution of animals, 292. 

of rainfall, 248, 249. 
Diurnal variations, 38. 
Dodo, 306. 
Dog, 293, 302. 
Doldrums, 223. 
Dormant volcanoes, 50. 
Dormice, 296. 
Drainage, 165-170, 319. 
Draught animals, 301. 
Drift, Antarctic, 196, 197. 

Atlantic, 213. 
Dromedary, 302. 
Drowned mines, 142. 



INDEX 



337 



Drumlin, 269, 271. 

Dry season, 255. 

Dublin, temperature of, 217. 

Duck mole, 298 

Ducks, 292. 

Dunes, 125, 227. 

at Ostend, 184. 
D'Urvillasa utilis, 287. 
Dust, in atmosphere, 200, 201, 206. 

volcanic, 50, 54. 
"Dust whirlwind," 234. 
Dyewoods, 291. 

Eagle, 292, 296. 
Earth, a magnet, 33. 

and the universe, 17. 

an oblate spheroid, 20. 

a planet, 11. 

attractive power of, 33. 

axis of, 23. 

curvature of, 18. 

density of, 21. 

fluidity of, 45. 

interior of, 45. 

internal heat of, 40. 

magnetic poles of, 33. 

magnetism of, 32. 

motions of, 23. 

nucleus of, 22. - 

revolution of, 23, 25. 

rotation of, 23, 25. 
Earthquakes, 60-69. 

causes of, 66. 

distribution of, 65. 

duration of, 61. 

sea waves caused by, 63, 64. 
East Australian current, 196. 
Ebb tide, 183. 
Eclipse of the moon, 19. 
Edwards plateau, 89. 
Egypt, floods of, 170. 
Elburz, Mount, 116. 
Elburz Mountains, 120. 
Electricity, atmospheric, 275. 
Electro-magnet, 32. 



Elephants, 292, 302. 
Elevation, continental, 91. 

effect of, 216. 
Elton, Lake, 161. 
Emu, 298, 305. 
England, cHmate of, 213. 
Epicentrum, in earthquakes, 60. 
Equator, 23. 

magnetic, 34. 
Equatorial Calm Belt, 223. 
Equatorial current, 192, 193, 194, 196, 

198. 
Equatorial zone of animal life, 292. 

vegetation, 284. 
Equinox, autumnal, 26. 

vernal, 27, 207. 
Equinoxes, 26, 27. 
Eratosthenes, problem of, 24. 
Eroded plateaus, 83. 
Erosion, 75, 83, 86, 99, 144-146. 
Eruptions, volcanic, 51-55. 
Esker, 271. 
Estacado, Llano, 82. 
Estuaries, 93. 
Eucalyptus, 310. 
Europe, coast line, 73. 

drainage of, 167. 

relief of, 114-118. 
Evaporation, 138, 139, 239. 
Everest, Mount, 119. 
Excessive rainfall, 255. 
Extension, 319. 
Extinct volcanoes, 50. 

Fahrenheit scale, 209. 
Fault, 60, 66. 
Faulting, 86. 
Field, magnetic, ^^. 
Figs, 309, 324- 
Finches, 299. 
Fiords, 93, 117. 
Firs, 291. 
Fishing, 326. 
Fissure springs, 141. 
Fixed stars, 11. 



338 



INDEX 



Flanks, mountain, 86. 

Flax, 291. 

Flood plain, 78. 

Flood tide, 183. 

Floods, 166. 

Fluidity of earth, 45. 

Flying fish, 308. 

Flying lemurs, 297. 

Fog, 195, 242. 

Folding, 86. 

Food plants, 288. 

Foothills, 76. 

Force of waves, 182. 

Forests, submerged, 93. 

Foxes, white, 292. 

Franz Josef glacier, 263, 265. 

Frigid zones, true, 217. 

Fringing reefs, 132. 

Fumaroles, 49. 

Ganges, delta of, 79. 
Garden of the Gods, 98. 
Gardens, 99. 
Garonne, bore of, 189. 
Geysers, 42. 
Ghats, 121. 
Giacobini's comet, 12. 
Ginger, 290. 
'GiraiTe, 297, 298. 
Glacial grooves, 270. 
Glacial motion, 262. 

causes of, 265. 

theory of, 264. 
Glacial period, 268. 

of North America, 269. 
Glaciers, 261. 

as river sources, 217. 

continental, 273. 

distribution of, 272. 

size of, 272. 
Globigerina, 178. 
Goats, 292, 296. 
Gobi, Desert of, 121. 
Godwin-Austen, mountain, 120. 
Gold Hill mines, temperature of, 40. 



Gorilla, 297. 

Gradient, 230. 

Graduating thermometers, 209. 

Graham Island, 47, 130. 

Grand Banks, fogs of, 195. 

Grand Canyon, 90, 91. 

Grand divisions, 71. 

Grand Geyser, 43. 

Grapes, 324. 

Gravity, specific, 198. 

Gravity springs, 141. 

Great Basin, 102. 

Great Geyser, 42. 

Great gray kangaroo, 301. 

Great Lakes, 164. 

Great Plains, 81. 

Great Salt Lake, 103, 159, 162. 

Grecian Peninsula, 116. 

Green Mountains, 104. 

Greenwich, 24. 

Gregorian calendar, 29. 

Gregory XIII, Pope, 29. 

Grenelle, temperature of well at, 41. 

Grizzly bear, 299, 302. 

Grooves, glacial, 270. 

Ground swell, 181. 

Ground waters, 140-144. 

Guiana, highland of, no. 

Guinea fowls, 297. 

Gulf Stream, 193, 194, 213. 

Gulf weed, 287. 

Gulls, 292. 

Gums, 291. 

Gushers, 42. 

Gutta-percha, 309. 

Hail, 201, 258. 

Halo, 278. 

Hammerfest, climate of, 213. 

temperature of, 195. 
Height, of the land, 75. 

of tides, 188. 

of waves, 180. 

and temperature, 213, 216. 
Helium, 200. 



INDEX 



339 



Hemp, 291, 324. 
Henderson meteorite, 13. 
Herbivorous animals, 282. 
Hercules, constellation, 17. 
High barometer, 205. 
Highlands, 76. 
High Sierra, 100. 
High tides, 183. 
Hills, 76. 

Himalayas, 119, 120. 
Hindu Kush, 120. 
Hippopotamus, 297. 
Honey bear, 297. 
Hoogly, bore of, 189. 
Horizon, 171. 

Horizontal zones of vegetation, 2S4. 
Horns, 86. 

Horse, 292, 296, 301. 
Horse latitudes, 223. 
Hot springs, 41, 42. 
Humboldt current, 197. 
Humboldt Lake, 103. 
Humidity, 239. 
Humming birds, 301. 
Hydrosphere, 21, 22, 70. 
Hypothesis, nebular, 14, 45. 
planetesimal, 14, 16, 202. 

Iberian Peninsula, 117. 
Ice, lighter than water, 137. 

melting point of, 45. 
Icebergs, 273. 
Iceland, springs in, 42. 
Inclination of needle, 34. 
India, flora of, 309. 

plains of, 123. 

rainfall of, 251. 
Indian corn, 288. 
Indian Ocean, 174-178. 

currents of, 197. 
Indians, American, 317. 
Indigenous civilization, 318. 
Industries of United States. 323. 
Inferior highland, 95. 
Inland cHmate, 211. 



Inland seas, 160, 161. 
Inorganic bodies, 280. 
Insular climate, 211. 
Interior plains, 76. 
Internal heat, 40. 
Inundations, 166. 
Iran, plateau of, 121. 
Iron Gate, 116. 
Irrigation, 256, 319, 320. 
Islands, 128-134. 

barrier, 182. 

continental, 128. 

coral, 130-134. 

oceanic, 129. 

volcanic, 130. 
Isobars, 205. 
Isoclinic lines, 36. 
Isogonic lines, 36. 
Isothermal lines, 216. 

and life, 293. 

map, 214-215. 
Italian Peninsula, 116. 

Jalap, 291. 
James River, 105. 
Japan, earthquakes in, 64, 65. 
Japan current, 196. 
Jetties, 148. 
Julian calendar, 29. 
Jungfrau, 115. 
Jupiter, IT. 
year of, 26. 

Kamerun Mountains, 124. 
Karnes, 271, 272. 
Kangaroo, 298. 
Karakoran Mountains, 120. 
Kashmir goat, 305. 
Kenia, Mount, 123. 
Khamsin, 226. 

Khaiia hills, rainfall of, 251. 
Khin-Gan Mountains, 121. 
Kilauea, 46. 

Kilimanjaro, Mount, 123. 
Killarney Lakes, 163. 



340 



INDEX 



Kirghiz Steppes, 122. 
Krakatoa, 54. 
Krypton, 200. 
Kuen-Lun, 120. 
Kuro-Shiwo, 196. 

Labor, distribution of, 322. 
Labrador, climate of, 213. 
Labrador current, 196. 
Laccolite, 88. 
Lagoon, 132. 

Lahontan, Lake, 103, 162. 
Lakes, 155-164. 

causes of, 155, 156. 

desiccated, 161-163. 

distribution of, 164. 

extinct, 103, 161-163. 

offices of, 163. 

salt, 158-162. 
Land, distribution of, 70-72. 
Land winds, 253. 
Latent heat, 137, 138. 
Lateral moraine, 267. 
Latitude, 23, 24. 
Latitudes, horse, 223. 
Lava, 49, so, 54, 55. 
Leap year, 29. 
Lemurs, 297. 
Lightning, 275. 

kinds of, 276. 
Lions, 292, 296. 
Lisbon earthquake, 65. 
Lithosphere, 21, 22, 70. 
Liverpool, tides at, 189. 
Livingstone Mountains, 123. 
Llama, 301, 304, 306. 
Llano Estacado, 82. 
Llanos, 76, in. 
Logwood, 291. 
Loma Point, 179, 180. 
Longitude, 2^, 24. 
Longitudinal valleys, 89. 
Low barometer, 205. 
Low tide, 183. 
Lowlands, 76. 



Lunar day, 183, 185. 
Lyre bird, 298. 

"Mackerel sky," 244. 
Macrocystis pyrifera, 287. 
Magdalena River, 108. 
Magnet, 32. 

Magnetic declination, 37. 
Magnetic equator, 34. 
Magnetic field, ^^. 
Magnetic needle, ^^. 
Magnetic north pole, 34. 
Magnetic parallels, 36. 
Magnetic poles, ^,2,. 
Magnetic storms, 38. 
Magnetism,* terrestrial, 32. 
Magpies, 296. 
Mahogany, 291. 
Maladetta, Mount, 116. 
Malay race, 317. 
Malay tiger, 304. 
Mai de montagne, 205. 
Man, races of, 314. 

range of, 311. 
Mandioca. See Manioc. 
Mango, 309. 
Manioc, 289, 310. 
Manufacturing, 325, 326. 
Maple, 291. 
Maravaca, no. 
Marine deposits, 176-178. 
Maritime chmate, 211. 
Marlin, temperature of well at, 41. 
Mars, n. 
Marsupials, 298. 

Materials for Physical Geography, 330. 
Matterhorn, the, 85, 116. 
Mauna Kea, 48. 
Meanders, 147, 148. 
Medial moraine, 267. 
Medicinal plants, 291. 
Mediterranean Sea, saltness of, 172. 
Melting point, 45. 
Menam valley, overflow of, 79. 
Mercurial barometer, 203. 



INDEX 



341 



Mercurial thermometer, 208. 
Mercury (quicksilver), 198, 203, 208. 
Mercury (planet), 11. 

year of, 26. 
Mer de Glace, 262. 
Meridians, 23. 
Mesa, 84. 

Meteoric swarms, 12, 14. 
Meteorite, Henderson, 13. 
Midday lines, 23. 
Millet, 288. 
Mineralization, 42. 
Minerva Terrace, 42. 
Mines, temperature of, 40. 
Mining, 326. 
Mirage, 278. 
Mississippi basin, 107. 
Mississippi River, amount of water 
in, 167. 

banks of, 150. 

delta of, 79, 149, 150. 

erosion by, 146. 

floods in, 163, 166. 

jetties of, 148. 

meanders of, 147. 
Mistral, 226. 
Mitchell, Mount, 105. 
Mocking bird, 299. 
Mock suns, 278. 
Moisture of the air, 239. 
Moles, 296. 
Mongolian race, 315. 
Monkeys, 301. 
Monsoons, 198, 224. 

effect of, 225. 

minor, 226. 
Mont Blanc, 116, 261. 

boiling point at, 204. 
Mont Cervin, 85. 
Mont Pelee, 54. 
Monte Rosa, 116. 
Monument Park, 99. 
Moon, eclipse of the, 19. 
Moondogs, 278. 
Moons, II. 



Moraine, 267. 
Motions of the earth, 23. 
Mot-mots, 30X. 
Mountain chain, 86. 
Mountain crest, 86. 
Mountain flanks, 86. 
Mountain knots, 108. 
Mountain peaks, 86. 
Mountain range, 86. 
Mountain sickness, 205. 
Mountain system, 86. 
Mountains, 76, 85, 95-127. 

formation of, 86. 

regulators of rainfall, 251. 

block, 88, 102, 104. 
Movements, earth, 75. 
Mozambique current, 197. 
Musk-ox, 292. 

Narcotics, 290. 

Natural magnet, 32. 

Neap tides, 187. 

Nebula, 15. 

Nebular hypothesis, 15, 45. 

Needle, magnetic, ^t,. 

dechnation of the, 36. 

dip of the, 34. 
Negro race, 316. 
Neptune, 11. 

year of, 26. 
Neutral line (magnetic), ^^. 
New Caledonia reefs, 132. 
New Madrid earthquake, 65. 
New River, 105. 
New Style, 29. 
New Zealand, springs in, 42. 
Newton, 25. 

Niagara Falls, 145, 152-156. 
Nightingales, 296. 
Nile River, 80, 169, 170. 

delta of, 149. 
Nile valley, overflow of, 79, 80. 
Nimbus, 246. 
Nitrogen, 200. 
North America, drainage of, 167. 



342 



INDEX 



North America, flora of, 310. 

glacial period, 269. 

rainfall of, 252. 

relief of, 95-107. 
North Cape, 117, 118. 
North Carolina, coastal map, 129. 
North Pacific current, 196. 
North pole, 24. 
North star, 24. 
Northern Hemisphere, 71. 
"Northers," 226. 
Norway, climate of, 213. 
Nucleus, earth's, 22. 
Nutmeg, 290. 

Oak, 291. 

Oases, 126. 

Oblate spheroid, earth an, 20. 

Ocean currents, 190, 191. 

affect climate, 212. 
Oceanic circulation, 197. 
Oceanic Islands, 129. 
Oceans, 104-178. See Sea.. 
Oil palm, 309. 
Old Faithful Geyser, 44. 
Olives, 309, 325. 
Olympus, Mountain, 116. 
Ooze, 178. 
Opium, 290. 
Opossums, 298, 299. 
Oranges, 325. 
Orang-outang, 297, 299. 
Orbits, 10. 
Orchard fruits, 324. 
Oregon, climate of, 213. 
Organic bodies, 280. 
Orinoco River, no, in. 

delta, 129. 
Orizaba, climate of, 216. 
Orkney Isles, temperature of, 195. 
Ostend, 184. 
Ostrich, 305. 
Ox, 292, 301. 
Oxbow, 147. 
Oxygen^ 200. 



Oysters, 308. 

Pacific current, 196. 
Pacific Highland, 95, 107. 
Pacific Ocean, 174-178. 
Pamir, 119. 
Pampas, 76, in. 
Pamperos, 226. 
Papandayang, 58. 
Parallels, 23. 

magnetic, 36. 
Paraselenae, 278. 
Parhelia, 278. 
Parime Mountains, no. 
Parks, 98, 99. 
Passes, 91. 
Passion flower, 310. 
Peacock, 298. 
Peaks, mountain, 86. 
Pear, 309. 
Pelee, Mont, 54. 
Pe-Ling Mountains, 120. 
Pepper, 290. 
Periodical rains, 254. 
Periodical winds, 224. 
Persimmon, 310. 
Peruvian current, 197. 
Pheasant, Argus, 298. 
Pheasants, 292, 296. 
Phosphorescence, in sea, 173. 
Physical features, 75. 
Physical geography, influenced by 
man, 319. 

manner of studying, 329. 

related to other sciences, 328. 

scope of, 32. 
Piedmont belt, 100. 
Pikes Peak, 97. 
Pimento, 290. 
Pines, 291. 
Plain, delta, 79. 
Plains, 76. 
Planetesimal hypothesis, 15, 16, 

201. 
Planetesimals, 16. 



INDEX 



343 



Planetoids, lo, 12. 
Planets, 11. 

relative sizes of, 16, 17, 21. 
Plants, distribution of, 282. 

higher, 280. 

medicinal, 291. 

used for clothing, 291. 
Plata River, no, in. 

no delta, 150. 
Plateaus, 76, 82-84. 

of Africa, 123-125. 

of Asia, 119, 121. 

of North America, 97, 100-104. 

of South "America, 108-110. 
Playas, 102. 
Po River, 150, 166. 
Point Loma, 179, 180. 
Pointers, 24. 
Poisonous serpents, 292. 
Polar currents, 192, 196. 
Polar vi^inds, 223. 
Polar zones of vegetation, 284. 
Poles, 24. 

magnetic, ^3- 
Polyps, 130, 131, 197. 
Pope Gregory XIII, 29. 
Position, 23. 
Potato, 289, 310. 
Potomac River, 105. 
Pouched rat, 299. 
Prairie dogs, 299. 
Prairies, 76, 107. 
Precipitation, 240. 
Prehensile-tailed monkey, 301. 
Prevailing winds and clilnate, 212. 
Problem of Eratosthenes, 24. 
Puma, 226. 
Pumice, 50. 
Pyramid Lake, 103. 
Pyrenees, 116. 

Quartz, in springs, 41. 
Quicksilver, weight of, 198. 
Quinine, 291. 
Quito, boiling point at, 204. 



Raccoons, 299. 
Race, tide, 188. 

Races of mankind, 312, 313, 314. 
Radiolaria, 178. 
Rain, 201. 
• cause of, 249. 

classification of, 253. 

constant, 254. 

deficient, 255. 

distribution of, 249. 

excessive, 255. 

periodical, 254. 

regulators of, 251. 
Rainbovv^s, 278. 
Rainless regions, 257. 
Rainy season, 255. 
Range, geographical, 282. 

mountain, 86. 

of draught animals, 301. 
Rapids, 150, 153. 
Rattlesnake, 299. 
Reclaimed land, 320. 
Red clay, 178. , 
Red Sea, saltness of, 172. 
Reefs, coral, 131, 1^2, 197. 
Reflection of light, 278. 
Refraction of light, 278. 
Regelation, 265. 
Regions, zoological, 292. 

of tife, 296. 
Reindeer, 292, 302. 
Relief of the land, 75. 

causes of, 93. 

continental, 95. 

effects of, 94. 

forms of, 76. 

of Africa, 123-126. 

of Asia, 1 19-123. 

of Australia, 126, 127. 

of Europe, 11 2-1 19. 

of North America, 95-107. 

of South America, 107-111. 
Reservoir, underground, 142. 
Return currents, 192. 
Revolution of the earth, 23, 25. 



344 



INDEX 



Rheas, 301, 305. 

Rhinoceroses, 292. 

Rhone River, matter transported by, 

146. 
Rice, 79, 288, 289, 324. 
River basin, 165. 
River plains, 76. 
River system, 144. 
Rivers, 165-170. 

sources of, 144, 271. 

tides of, 189. 
Robins, 299. 
Rocky Mountains, 97. 
Rosa, Monte, 116. 
Rosewood, 291. 
Rotation of the earth, 23, 25. 
Ruwenzori Mountains, 123. 
Rye, 288. 

Sables, 292. 
Sahara, 125. 

climate of, 212. 
Saint Elmo's Fire, 278. 
Saint Gotthard tunnel, temperature 

of, 40. 
Saint Michael, springs at, 41. 
Salt, in sea, 171, 172. 
Sand, volcanic, 50, 53. 
Sand dune, 125, 227. 
Sandalwood, 291. 
San Francisco earthquake, 63, 66, 68, 

69. 
San Francisco River, no. 
Santo rini, 130. 
Sargasso Seas, 199. 
Sarsaparilla, 291, 310. 
SateUites, 11. 
Saturation, point of, 239. 
Saturn, 11. 

and his rings, 15. 
Scales, thermometer, 209. 
Scandinavian Mountains, 117. 
Sea, 1 71-178. 

bottom of, 175-177. 

color of, 172. 



Sea, currents of the, 192. 

depth of, 174, 175- 

extent of, 171. 

phosphorescence of, 173. 

saltness of, 171, 172. 

temperature of, 174. 
Sea waves, earthquake, 63, 64. 
Sea winds, 253. 
Seal, 292, 308. 
Seasonal variation in temperature, 

207. 
Seasons, change of, 29. 
Secretary bird, 297. 
Secular variations, 38. 
Sequoia gigantea, 310. 
Serpents, poisonous, 292. 
Sharks, 308. 
Sheep, 292, 296. 
Sheet lightning, 276. 
Shooting stars, 14. 
Shore Hnes, delta, 79. 
Shoshone Falls, 155. 
Siam, rice crop of, 79. 
Siberian Plain, 122. 
Sidereal day, 28. 
Sierra, 86. 
Sierra, High, 100. 
Sierra Nevada, 100. 
Silica in geysers, 43. 

in springs, 41. 
Sihcious ooze, 178. 
Silt, 146. 
Silvas, 76, no. 
Silver-tip grizzly bear, 302. 
Simoom, 235. 
Sinter, 41. 
Sirocco, 226. 
Skaptar Jokul, 54. 
Skunks, 299. 
Sloth, 301, 305. 
Snake River, loi, 155. 
Snow, 201, 258. 

uses of, 259. 
Snow line, 258. 
Snow Mountains, 123. 



INDEX 



345 



Soft rocks, erosion of, 84. 
. Solar day, 28. 
Solar system, 10, 11. 

origin of, 14. 
Solstice, winter, 27. 
Solstices, 26. 
South America, drainage of, 167, i( 

flora of, 310. 

rainfall of, 251. 

relief of, 107-111. 
South magnetic pole, 34. 
South pole, 24. 
Southern Hemisphere, 71. 
Spanish peninsula, 116. 
Specific gravity, 198. 
Sperm whale, 308. 
Spheroid, oblate, 20. 
Spices, 290. 
Spits, 182. 
Sponges, 308. 

Spot period of the sun, 39. 
Spring tides, 183, 185. 
Springs, 140, 141. 

hot, 41. 

algas in, 42. 
Standard time, 28. 
Stars, fixed, 11. 

shooting, 14. 
Steppes, 76, 122. 
Storm cards, 231. 
Storm laws, value of, 233. 
Storms, 229. 

areas of, 233. 

cause of, 229. 

distribution of, 235. 

laws of, 231. 
Storms, magnetic, 38. 
Strata, dip of, 77, 78. 
Stratus cloud, 245. 
Stromboli, 50, 52. 
Submerged forests, 93. 
Subsidence of land, 92. 
Sugar, 324. 
Sugar cane, 290, 293. 
Sulaiman Mountains, 121. 



Sun, 14. 

spot period of, 39. 
Sundogs, 278. 
Superior, Lake, 164. 
Superior highland, 95. 
Susquehanna River, 105. 
Sweet potato, 309. 
Sycamore fig, 309. 
System, mountain, 85. 

Table-lands, 76, 82. 
Tahiti, 134. 
Tailor birds, 298. 
Tea, 290. 
Teak, 291, 309. 
Telegraphic plateau, 176. 
Temperate zone, of animal life, 292. 
Temperate zones, of vegetation, 284. 

true, 217. 
Temperature, atmospheric, 205. 

measuring, 208. 

seasonal, 207. 

of zones of, 217. , 

of artesian wells, 41. 

of Calumet-Hecla mine, 40. 

of Comstock lode, 40. 

of Gold Hill mines, 40. 

of Gulf Stream, 194. 

of Hammerfest, 195. 

of Orkney Isles, 195. 

of Saint Gotthard tunnel, 40. 

of Werchojausk, 212. 

and cHmate, 210. 

and height, 213, 216. 
Terminal moraine, 26. 
Terraces, 92. 

Terrestrial magnetism, 32. 
Thermal springs, 41. 
Thermometer, 203, 208. 
Thian Shan, 120. 
Thrushes, 299. 
Thunder, 276. 
Tibet, plateau of, 82, 119. 
Tidal wave, movement of, 187. 
Tides, 183. 



346 



INDEX 



Tides, height of, i88. 

neap, 187. 

spring, 185. 

of rivers, 180. 
Tide-water country, 324. 
Tigers, 292, 297, 304. 
Till, 269. 

Time, standard, 28. 
Titicaca, Lake, to8. 
Tobacco, 290. 
Todies, 301. 
Tomboro, 58. 
Tornado, 234. 
Tornadoes, 233. 
Torricelli's experiment, 202. 
Torrid Zone, true, 217. 
Toucans, 301. 
Trade winds, 221. 
Transportation, 146. 
Transporting agents, 182. 
Transverse valleys, 89. 
Tree kangaroo, 298. 
Trees, useful, 291. 
Trogon, 298. 
Tropic of Cancer, 30. 
Tropic of Capricorn, 31. 
Trough of wave, 179. 
Tsien-tang, bore of, 189, 192. 
Tufa, 162. 
Turkestan, 121. 
Turkey, 292. 
Tuscarora deep, 175. 

Universe, earth and the, 17. 
Upward fold, 87. 
Uranus, 11. 
Ural Mountains, 117. 
Useful trees, 291. 

Valdai Hills, 118. 
Valleys, 89. 
Vampire bat, 301. 
Vapor, water, 201. 
Variable winds, 221, 255. 
Variations, diurnal, 38. 



Variations in decHnation, 38. 

in pressure, 204. 

secular, 38. 
Vegetables modified by climate, 283. 
Vegetation, zones of, 283. 
Velocity, of clouds, 247. 

of wave movements, 181. 
Venus, II. 

Vernal equinox, 26, 207. 
Vertical zones of vegetation, 286. 
Vesuvius, 48, 50-53, 54. 
Victoria Falls, 155. 
Victoria Lake, 164. 
Victoria Regia, 281. 
Vicuna, 304. 

Vindhya Mountains, 121. 
Volcanic cones, 46.-48. 
Volcanic islands, 129, 130. 
Volcanoes, 43, 46-59. 

causes, 58-59. 

classified, 50. 

distribution of, 55-58. 

eruptions, 51-55, 58. 

products, 48-50. 
Volga, delta, 149. 
Vulcanic plateaus, 82. 
Vulcanism, 86. 

Walker Lake, 103. 
Walnut, 291. 
Walrus, 292. 

Washington, Mount, 105. 
Water, absorption of heat, 137. 

circulation of, 139. 

composition of, 136. 

evaporation and condensation of, 

138, 139- 

expansion of, 136. 

forms of, 136. 

properties of, 136-139. 

solvent power of, 138. 
Waterfalls, 151- 15 7. 
Water gap, 91. 
Waters of the land, 140-164. 
Watershed, 165. 



INDEX 



347 



Waterspout, 235. 
Wave, tidal, 187. 

Wave action, on rocky headland, 
182. 

on submerged rocks, 181. 
Wave movements, velocity of, 181. 
Waves, 179. 

force of, 182. 

height of, 180. 
Weather and climate, 210. 
Weather forecasts, 237. 
Weather map, 236. 

description of, 238. 
Weaver birds, 297. 
Wells, temperature of artesian, 41. 
Werchojausk, climate of, 212. 
West Indian boa, 309. 
WesterHes, prevailing, 221. 
Whale, 292, 308. 

right, 308. 
Wheat, 288, 324. 
Whirlpool, 189. 
Whirlwind, 233. 
"Whirlw^ind, dust. 
White bear, 292. 
White foxes, 292. 
White Mountains, 
Whitsunday Island, 133. 
Wicklow, tides at, 189. 
"Wind roads," 234. 



234- 



104. 



Winds, 218. 

affect climate, 212. 

cause of, 218. 

constant, 221. 

periodical, 223. 

polar, 223. 

surface effects of, 227. 

trade, 221. 

variable, 221, 255. 
Winnenucca Lake, 103. 
Wolf, 292, 296. 
Wombat, 298. 
Wrens, 299. 
Wyoming, springs in, 42. 

Yak, 305. 

Yellowstone, Falls of, 155. 

Yellowstone National Park, springs 

and geysers in, 42, 44. 
Yosemite Falls, 155, 157. 

Zagros Mountains, 121. 
Zambezi River, fails on, 155. 
Zenith, 24. 

Zigzag lightning, 276. 
Zones, of animal life, 292. 

of temperature, 217. 

of vegetation, 283. 
Zoological regions, 292, 294, 295. 



TYPOGRAPHY BY THE J. S. GUSHING COiMPANY, NORWOOD, MASS. 



'Ai^ i4\K)^ 




021 648 945 





